{"id":100603,"date":"2026-09-04T21:57:01","date_gmt":"2026-09-04T13:57:01","guid":{"rendered":"https:\/\/www.wsisp.com\/helps\/100603.html"},"modified":"2026-09-04T21:57:01","modified_gmt":"2026-09-04T13:57:01","slug":"mysql","status":"publish","type":"post","link":"https:\/\/www.wsisp.com\/helps\/100603.html","title":{"rendered":"MySQL"},"content":{"rendered":"

\u4e00，\u6570\u636e\u5e93<\/h3>\n

1，\u6570\u636e\u5e93\u7684\u597d\u5904： （1）\u5b9e\u73b0\u6570\u636e\u6301\u4e45\u5316 （2）\u4f7f\u7528\u5b8c\u6574\u7684\u7ba1\u7406\u7cfb\u7edf\u540c\u610f\u7ba1\u7406，\u4fbf\u4e8e\u67e5\u8be2 2，\u6570\u636e\u5e93\u7684\u6982\u5ff5 （1）\u6570\u636e\u5e93（database）\u7b80\u79f0 DB （2）\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf（DBMS) （3）\u7ed3\u6784\u5316\u67e5\u8be2\u8bed\u8a00(SQL)<\/p>\n\n\u5c42\u7ea7\u7ec4\u4ef6\u8bf4\u660e<\/tr>\n\n\n\n\n
\u7b2c\u4e00\u5c42<\/td>\n\u5e94\u7528\u7a0b\u5e8f（App）<\/td>\n\u7528\u6237\u76f4\u63a5\u4f7f\u7528\u7684\u8f6f\u4ef6，\u901a\u8fc7 SQL \u6216 API \u4e0e DBMS \u4ea4\u4e92<\/td>\n<\/tr>\n
\u7b2c\u4e8c\u5c42<\/td>\n\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf（DBMS）<\/td>\n\u6838\u5fc3\u8f6f\u4ef6（\u5982 MySQL），\u8d1f\u8d23\u67e5\u8be2\u5904\u7406\u3001\u4e8b\u52a1\u7ba1\u7406\u3001\u5b58\u50a8\u7ba1\u7406\u3001\u5b89\u5168\u7ba1\u7406<\/td>\n<\/tr>\n
\u7b2c\u4e09\u5c42<\/td>\n\u5b9e\u9645\u5b58\u50a8\u7684\u6570\u636e<\/td>\n\u78c1\u76d8\u4e0a\u7684\u7269\u7406\u6587\u4ef6，\u7531 DBMS \u7edf\u4e00\u7ba1\u7406<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

3，\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf （1）MySQL （2）Oracle （3）SQL Server （4）PostgreSQL （5）MongoDB<\/p>\n

4，\u6570\u636e\u5e93\u50a8\u5b58\u6570\u636e\u7684\u7279\u70b9 \u5c06\u6570\u636e\u653e\u8868\u4e2d，\u8868\u653e\u5728\u5e93\u4e2d<\/p>\n

\u4e8c，Linux\u4e2d\u4e0b\u8f7dMySQL<\/h3>\n

1，MySQL\u5b89\u88c5\u7248\u672c：8.x<\/p>\n

# \u5378\u8f7d\u51b2\u7a81\u8f6f\u4ef6<\/span>
\nrpm –<\/span>e –nodeps `rpm -qa|grep mariadb`<\/span>
\nrpm –<\/span>e –nodeps `rpm -qa|grep mysql`<\/span><\/p>\n

# \u79bb\u7ebf\u5b89\u88c5mysql<\/span>
\nrpm –<\/span>ivh mysql–<\/span>community–<\/span>common–<\/span>8.0<\/span>.34<\/span>–<\/span>1.<\/span>el7.<\/span>x86_64.<\/span>rpm
\nrpm –<\/span>ivh mysql–<\/span>community–<\/span>client–<\/span>plugins–<\/span>8.0<\/span>.34<\/span>–<\/span>1.<\/span>el7.<\/span>x86_64.<\/span>rpm
\nrpm –<\/span>ivh mysql–<\/span>community–<\/span>libs–<\/span>8.0<\/span>.34<\/span>–<\/span>1.<\/span>el7.<\/span>x86_64.<\/span>rpm
\nrpm –<\/span>ivh mysql–<\/span>community–<\/span>libs–<\/span>compat–<\/span>8.0<\/span>.34<\/span>–<\/span>1.<\/span>el7.<\/span>x86_64.<\/span>rpm
\nrpm –<\/span>ivh mysql–<\/span>community–<\/span>client–<\/span>8.0<\/span>.34<\/span>–<\/span>1.<\/span>el7.<\/span>x86_64.<\/span>rpm
\nrpm –<\/span>ivh mysql–<\/span>community–<\/span>icu–<\/span>data<\/span>–<\/span>files–<\/span>8.0<\/span>.34<\/span>–<\/span>1.<\/span>el7.<\/span>x86_64.<\/span>rpm
\nrpm –<\/span>ivh mysql–<\/span>community–<\/span>server–<\/span>8.0<\/span>.34<\/span>–<\/span>1.<\/span>el7.<\/span>x86_64.<\/span>rpm<\/p>\n

# \u521d\u59cb\u5316<\/span>
\nmysqld –initialize <\/span>
\n# \u6539\u6743\u9650<\/span>
\nchown –<\/span>R mysql:mysql \/<\/span>var\/<\/span>lib\/<\/span>mysql
\n# \u542f\u52a8MySQL<\/span>
\nsystemctl start<\/span> mysqld.<\/span>service
\n# \u67e5\u770b\u72b6\u6001<\/span>
\nsystemctl status<\/span> mysqld.<\/span>service
\n# \u5f00\u673a\u81ea\u542f\u52a8<\/span>
\nsystemctl enable<\/span> mysqld.<\/span>service
\n# \u83b7\u53d6\u521d\u59cb\u5bc6\u7801<\/span>
\ngrep "password"<\/span> \/<\/span>var\/<\/span>log\/<\/span>mysqld.<\/span>log
\n# \u767b\u5f55Mysql<\/span>
\nmysql –<\/span>uroot –<\/span>p\u5bc6\u7801
\n# \u4fee\u6539\u5bc6\u7801<\/span>
\nALTER<\/span> USER<\/span> 'root'<\/span>@'localhost'<\/span> IDENTIFIED BY<\/span> '123456'<\/span>;<\/span>
\nALTER<\/span> USER<\/span> 'root'<\/span>@'localhost'<\/span> IDENTIFIED WITH<\/span> mysql_native_password BY<\/span> '123456'<\/span>;<\/span>
\n# \u5237\u65b0\u6743\u9650<\/span>
\nFLUSH PRIVILEGES<\/span>;<\/span>
\n# \u9000\u51fa<\/span>
\nexit<\/span>
\n# \u5207\u6362\u6570\u636e\u5e93<\/span>
\nUSE<\/span> mysql;<\/span>
\n# \u67e5\u770b\u7528\u6237<\/span>
\nSELECT<\/span> user<\/span>,<\/span>host,<\/span>plugin,<\/span>authentication_string FROM<\/span> user<\/span>;<\/span>
\n# \u521b\u5efa\u65b0\u7528\u6237<\/span>
\nCREATE<\/span> user<\/span> 'root'<\/span>@'%'<\/span>;<\/span>
\n# \u8bbe\u7f6e\u5bc6\u7801<\/span>
\nALTER<\/span> USER<\/span> 'root'<\/span>@'%'<\/span> IDENTIFIED BY<\/span> '123456'<\/span>;<\/span>
\nALTER<\/span> USER<\/span> 'root'<\/span>@'%'<\/span> IDENTIFIED WITH<\/span> mysql_native_password BY<\/span> '123456'<\/span>;<\/span>
\n# \u589e\u52a0\u5e93\u548c\u8868\u7684\u6743\u9650<\/span>
\nGRANT<\/span> ALL<\/span> PRIVILEGES<\/span> ON<\/span> *<\/span>.<\/span>*<\/span> TO<\/span> 'root'<\/span>@'%'<\/span>;<\/span>
\nFLUSH PRIVILEGES<\/span>;<\/span><\/p>\n

\u4e09，MySQL<\/h3>\n

MySQL\u662f\u76ee\u524d\u6700\u6d41\u884c\u7684\u5f00\u6e90\u5173\u7cfb\u578b\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf（RDBMS）\u3002\u5b83\u4f7f\u7528 SQL（\u7ed3\u6784\u5316\u67e5\u8be2\u8bed\u8a00）\u8fdb\u884c\u6570\u636e\u5e93\u64cd\u4f5c\u3002<\/p>\n

1，MySQL\u7684\u5165\u95e8\u4f7f\u7528 \u67e5\u770b\u72b6\u6001：systemctl status mysqld.service \u542f\u52a8：systemctl start mysqld \u505c\u6b62：systemctl stop mysqld \u767b\u5f55：mysql -u\u7528\u6237\u540d -p\u5bc6\u7801 \u9000\u51fa：exit\/quit 2，MySQL\u5e38\u7528\u547d\u4ee4 \u67e5\u770b\u5f53\u524d\u6570\u636e\u5e93：show database \u8fdb\u5165\u6307\u5b9a\u5e93：use \u5e93\u540d \u67e5\u770b\u5f53\u524d\u5e93\u4e2d\u6240\u6709\u8868：show tables \u67e5\u770bmysql\u7248\u672c：mysql –version\/select version() 3,MySQL\u8bed\u6cd5\u89c4\u8303 \u4e0d\u533a\u5206\u5927\u5c0f\u5199，\u4f46\u662f\u5efa\u8bae\u5173\u952e\u5b57\u5927\u5199，\u8868\u540d，\u5b57\u6bb5\u540d\u5c0f\u5199 \u6bcf\u6761SQL\u8bed\u53e5\u7528\u5206\u53f7\u7ed3\u675f \u8fdb\u884c\u7f29\u8fdb \u5355\u884c\u6ce8\u91ca：#\/\u2013 \u591a\u884c\u6ce8\u91ca：\/**\/ 4，DQL\u8bed\u8a00 \u4e0b\u8868\u662f\u6211\u6570\u636e\u5e93\u4e2d\u8868\u7684\u4fe1\u606f<\/p>\n\n\u8868\u540d\u52171\u52172\u52173\u52174\u52175\u52176\u52177\u52178\u52179\u521710\u521711<\/tr>\n\n\n\n\n\n\n\n\n
beauty<\/td>\nid<\/td>\nname<\/td>\nsex<\/td>\nboyfriend_id<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/tr>\n
boys<\/td>\nid<\/td>\nboyName<\/td>\nuserCP<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/tr>\n
departments<\/td>\ndepartment_id<\/td>\ndepartment_name<\/td>\nmanager_id<\/td>\nlocation_id<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/tr>\n
employees<\/td>\nemployee_id<\/td>\nfirst_name<\/td>\nlast_name<\/td>\nemail<\/td>\nphone_number<\/td>\njob_id<\/td>\nsalary<\/td>\ncommission_pct<\/td>\nmanager_id<\/td>\ndepartment_id<\/td>\nhiredate<\/td>\n<\/tr>\n
jobs<\/td>\njob_id<\/td>\njob_title<\/td>\nmin_salary<\/td>\nmax_salary<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/tr>\n
job_grades<\/td>\ngrade_level<\/td>\nlowest_sal<\/td>\nhighest_sal<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/tr>\n
locations<\/td>\nlocation_id<\/td>\nstreet_address<\/td>\npostal_code<\/td>\ncity<\/td>\nstate_province<\/td>\ncountry_id<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

（1）\u57fa\u7840\u67e5\u8be2<\/p>\n

select<\/span> \u67e5\u8be2\u5217\u8868 from<\/span> \u8868\u540d;<\/span>
\n–\u67e5\u8be2\u6240\u6709<\/span>
\nselect<\/span> *<\/span> from<\/span> \u8868\u540d;<\/span>
\n–\u8d77\u522b\u540d AS(\u53ef\u4ee5\u7701\u7565\u5e76\u4f7f\u7528\u7a7a\u683c\u66ff\u4ee3)，\u663e\u793a\u7684\u7ed3\u679c\u5b57\u7b26\u4e32\u4e2d\u6709\u7a7a\u683c\u9700\u8981\u52a0\u5f15\u53f7，\u5426\u5219\u62a5\u9519<\/span>
\nselect<\/span>
\n first_name AS<\/span> \u540d,<\/span>
\n last_name \u59d3
\nfrom<\/span>
\n employees;<\/span>
\n –\u53bb\u91cd DISTINCT<\/span>
\nselect<\/span> DISTINCT<\/span> \u67e5\u8be2\u5217\u8868 from<\/span> \u8868\u540d;<\/span>
\n\/*
\n 1\u3001\u4e24\u4e2a\u64cd\u4f5c\u6570\u90fd\u4e3a\u6570\u503c\u578b，\u5219\u505a\u52a0\u6cd5\u8fd0\u7b97
\n 2\u3001\u53ea\u8981\u5176\u4e2d\u4e00\u65b9\u4e3a\u5b57\u7b26\u578b，\u8bd5\u56fe\u5c06\u5b57\u7b26\u578b\u6570\u503c\u8f6c\u6362\u6210\u6570\u503c\u578b\u3002
\n \u5982\u679c\u8f6c\u6362\u6210\u529f，\u5219\u7ee7\u7eed\u505a\u52a0\u6cd5\u8fd0\u7b97，\u5982\u679c\u8f6c\u6362\u5931\u8d25，\u5219\u5c06\u5b57\u7b26\u578b\u6570\u503c\u8f6c\u6362\u62100\u540e\u518d\u505a\u8fd0\u7b97\u3002
\n 3\u3001\u53ea\u8981\u5176\u4e2d\u4e00\u65b9\u4e3a null，\u5219\u7ed3\u679c\u80af\u5b9a\u4e3anull
\n*\/<\/span>
\nselect<\/span> 66<\/span> +<\/span> '\u4e5d\u5341'<\/span>;<\/span>
\nselect<\/span> null<\/span> +<\/span> 10<\/span>;<\/span>
\n–concat()\u51fd\u6570<\/span>
\nselect<\/span> CONCAT(<\/span>'h'<\/span>,<\/span>'e'<\/span>,<\/span>'l'<\/span>,<\/span>'l'<\/span>,<\/span>'o'<\/span>)<\/span> as<\/span> \u7ed3\u679c;<\/span>–\u7ed3\u679c\u4e3aholle\u8fde\u5728\u4e00\u8d77<\/span>
\nSELECT<\/span> CONCAT(<\/span>last_name,<\/span>first_name)<\/span> AS<\/span> \u59d3\u540d FROM<\/span> employees;<\/span>
\n–\u663e\u793a\u8868 departments \u7684\u7ed3\u6784<\/span>
\ndesc<\/span> departments;<\/span>
\n— 6\u3001\u663e\u793a\u51fa\u8868 employees \u7684 first_name\u3001last_name\u3001job_id\u3001commission_pct \u5217，\u5404\u4e2a\u5217\u4e4b\u95f4\u7528\u9017\u53f7\u8fde\u63a5，\u5217\u5934\u663e\u793a\u6210 OUT_PUT<\/span>
\n— ifnull(expr1, expr2)<\/span>
\n–\u5982\u679c expr1 \u4e0d\u662f NULL，\u5219\u8fd4\u56de expr1；<\/span>
\n–\u5982\u679c expr1 \u662f NULL，\u5219\u8fd4\u56de expr2\u3002<\/span>
\nSELECT<\/span>
\n CONCAT(<\/span>first_name,<\/span>","<\/span>,<\/span>last_name,<\/span>","<\/span>,<\/span>job_id,<\/span>","<\/span>,<\/span>ifnull(<\/span>commission_pct,<\/span>0<\/span>)<\/span>)<\/span> as<\/span> OUT_PUT
\nFROM<\/span>
\n employees;<\/span><\/p>\n

（2）\u6761\u4ef6\u67e5\u8be2 [– \u6761\u4ef6\u67e5\u8be2\u603b\u7ed3\u8bed\u6cd5\u683c\u5f0f： \u2013 select \u2013 \u67e5\u8be2\u5217\u8868(3) \u2013 from \u2013 \u8868\u540d(1) \u2013 where \u2013 \u7b5b\u9009\u6761\u4ef6(2);<\/p>\n

\u2013 \u7b5b\u9009\u6761\u4ef6\u5206\u7c7b： \u2013 （1）\u6309\u6761\u4ef6\u8868\u8fbe\u5f0f\u7b5b\u9009 \u2013 \u7b80\u5355\u6761\u4ef6\u8fd0\u7b97\u7b26：> \u3001< \u3001>=\u3001<=\u3001!=(<>) \u2013 （2）\u6309\u903b\u8f91\u8868\u8fbe\u5f0f\u7b5b\u9009 \u2013 &&(and)\u3001||(or)\u3001!(not) \u2013 &&(and):\u4e24\u4e2a\u6761\u4ef6\u90fd\u4e3atrue，\u7ed3\u679c\u4e3atrue，\u53cd\u4e4b\u4e3afalse \u2013 ||(or)：\u53ea\u8981\u6709\u4e00\u4e2a\u6761\u4ef6\u4e3atrue，\u7ed3\u679c\u4e3atrue，\u53cd\u4e4b\u4e3afalse \u2013 !(not)：\u5982\u679c\u8fde\u63a5\u7684\u6761\u4ef6\u672c\u8eab\u4e3afalse，\u7ed3\u679c\u4e3atrue，\u53cd\u4e4b\u4e3afalse \u2013 （3）\u6a21\u7cca\u67e5\u8be2 \u2013 LIKE\u3001BETWEEN \u2026 AND \u2026\u3001IN()\u3001IS\u3001IS NOT\u3001\u3001IS NOT NULL\u3001IS NULL \u2013 LIKE：\u4e00\u822c\u548c\u901a\u914d\u7b26\u642d\u914d\u4f7f\u7528 \u2013 \u901a\u914d\u7b26： \u2013 % \u4efb\u610f\u591a\u4e2a\u5b57\u7b26，\u5305\u542b0\u4e2a\u52a0\u7c97\u6837\u5f0f\u5b57\u7b26 \u2013 _ \u4efb\u610f\u5355\u4e2a\u5b57\u7b26\u52a0\u7c97\u6837\u5f0f \u2013 BETWEEN \u2026 AND \u2026：\u5305\u542b\u4e24\u4e2a\u4e34\u754c\u503c，\u4e24\u4e2a\u4e34\u754c\u503c\u4e0d\u8981\u8c03\u6362\u987a\u5e8f，\u63d0\u9ad8\u8bed\u6cd5\u7684\u7b80\u6d01\u5ea6\u3002 \u2013 IN()：\u5224\u65ad\u67d0\u4e2a\u5b57\u6bb5\u7684\u503c\u662f\u5426\u5c5e\u4e8ein\u5217\u8868\u4e2d\u7684\u67d0\u4e00\u9879，in\u5217\u8868\u7684\u503c\u7c7b\u578b\u5fc5\u987b\u4e00\u81f4\u6216\u517c\u5bb9，\u63d0\u9ad8\u8bed\u6cd5\u7684\u7b80\u6d01\u5ea6\u3002 \u2013 IS NULL：is null \u6216\u8005 is not null \u5224\u65ad\u63a7\u5236，\u6ce8\u610f：= \u6216 <>\/!= \u4e0d\u80fd\u5224\u65adnull\u503c\u3002]<\/p>\n

select<\/span>
\n \u67e5\u8be2\u5217\u8868 （3<\/span>）
\nfrom<\/span>
\n \u8868\u540dv （1<\/span>）
\nwhere<\/span>
\n \u7b5b\u9009\u6761\u4ef6 （2<\/span>）
\n\/*
\n\u7b5b\u9009\u6761\u4ef6\u5206\u7c7b
\n（1）\u6309\u6761\u4ef6\u8868\u8fbe\u5f0f\u7b5b\u9009
\n\u7b80\u5355\u6761\u4ef6\u8fd0\u7b97\u7b26： >\u3001<\u3001=\u3001!= (<>)\u3001>=\u3001<=
\n（2）\u6309\u903b\u8f91\u8868\u8fbe\u5f0f\u7b5b\u9009
\n\u903b\u8f91\u8fd0\u7b97\u7b26： &&（and）\u3001|| （or）\u3001!（not）
\n&&（and）：\u4e24\u4e2a\u6761\u4ef6\u90fd\u4e3atrue，\u7ed3\u679c\u4e3atrue，\u53cd\u4e4b\u4e3afalse
\n||（or）：\u53ea\u8981\u6709\u4e00\u4e2a\u6761\u4ef6\u4e3atrue，\u7ed3\u679c\u4e3atrue，\u53cd\u4e4b\u4e3afalse
\n!（not）：\u5982\u679c\u8fde\u63a5\u7684\u6761\u4ef6\u672c\u8eab\u4e3afalse，\u7ed3\u679c\u4e3atrue，\u53cd\u4e4b\u4e3afalse
\n（3）\u6a21\u7cca\u67e5\u8be2
\nlike\u3001between and\u3001in\u3001is null
\n*\/<\/span>
\n–\u6309\u6761\u4ef6\u8868\u8fbe\u5f0f\u7b5b\u9009<\/span>
\nSELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n salary ><\/span> 12000<\/span>;<\/span>
\n–\u6309\u903b\u8f91\u8868\u8fbe\u5f0f\u7b5b\u9009<\/span>
\n#eg:\u67e5\u8be2\u5de5\u8d44\u572810000\u523020000\u4e4b\u95f4\u7684\u5458\u5de5\u540d\u3001\u5de5\u8d44\u4ee5\u53ca\u5956\u91d1 （\u5956\u91d1\u4f7f\u7528\u5956\u91d1\u7387\u66ff\u4ee3）<\/span>
\nSELECT<\/span>
\n first_name,<\/span>
\n salary,<\/span>
\n commission_pct
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n salary >=<\/span> 10000<\/span> and<\/span> salary <=<\/span>20000<\/span>;<\/span>
\n–\u6a21\u7cca\u67e5\u8be2<\/span>
\n# eg:\u67e5\u8be2\u5458\u5de5\u540d\u4e2d\u5305\u542b\u5b57\u7b26a\u7684\u5458\u5de5\u4fe1\u606f<\/span>
\nSELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n first_name like<\/span> '%a%'<\/span>;<\/span>
\n# eg:\u67e5\u8be2\u5458\u5de5\u540d\u4e2d\u7b2c\u4e09\u4e2a\u5b57\u7b26\u4e3ae，\u7b2c\u4e94\u4e2a\u5b57\u7b26\u4e3aa\u7684\u5458\u5de5\u540d\u548c\u5de5\u8d44<\/span>
\nSELECT<\/span>
\n first_name,<\/span>
\n salary
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n first_name like<\/span> '__e_a%'<\/span>;<\/span>
\n# eg:\u67e5\u8be2\u5458\u5de5\u59d3\u4e2d\u7b2c\u4e8c\u4e2a\u5b57\u7b26\u4e3a _ \u7684\u5458\u5de5\u540d\u548c\u5458\u5de5\u59d3<\/span>
\nSELECT<\/span>
\n first_name,<\/span>
\n last_name
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n last_name like<\/span> '_\\\\_%'<\/span>;<\/span>
\n# eg:\u67e5\u8be2\u5458\u5de5\u7f16\u53f7\u5728100\u5230200\u4e4b\u95f4\u7684\u5458\u5de5\u4fe1\u606f<\/span>
\nSELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n employee_id BETWEEN<\/span> 100<\/span> AND<\/span> 200<\/span>;<\/span>
\n# eg:\u67e5\u8be2\u5458\u5de5\u5de5\u79cd\u7f16\u7801\u662f：IT_PROG\u3001AD_ASST\u3001AD_VP \u4e2d\u7684\u4e00\u4e2a\u5458\u5de5\u540d\u548c\u5de5\u79cd\u7f16\u53f7\u3002<\/span>
\nSELECT<\/span>
\n first_name,<\/span>
\n job_id
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n job_id in<\/span>(<\/span>'IT_PROG'<\/span>,<\/span>'AD_ASST'<\/span>,<\/span>'AD_VP'<\/span>)<\/span>;<\/span>
\n# eg:\u67e5\u8be2\u6ca1\u6709\u5956\u91d1\u7684\u5458\u5de5\u540d\u548c\u5956\u91d1\u7387<\/span>
\nSELECT<\/span>
\n first_name,<\/span>
\n commission_pct
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n commission_pct is<\/span> null<\/span>;<\/span> <\/p>\n

SELECT<\/span>
\n first_name,<\/span>
\n commission_pct
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n commission_pct <=><\/span> null<\/span>;<\/span>
\n# is null VS <=><\/span>
\n# is null \u4ec5\u4ec5\u53ef\u4ee5\u5224\u65adnull\u503c，\u53ef\u8bfb\u6027\u8f83\u9ad8，\u5efa\u8bae\u4f7f\u7528<\/span>
\n# <=> \u65e2\u53ef\u4ee5\u5224\u65adnull\u503c，\u53c8\u53ef\u4ee5\u5224\u65ad\u666e\u901a\u7684\u6570\u503c，\u53ef\u8bfb\u6027\u8f83\u4f4e，\u4e0d\u5efa\u8bae\u4f7f\u7528\u3002<\/span><\/p>\n

(3)\u6392\u5e8f\u67e5\u8be2 [\u6392\u5e8f\u67e5\u8be2\u603b\u7ed3\u8bed\u6cd5\u683c\u5f0f： \u2013 select \u2013 \u67e5\u8be2\u5217\u8868 (3) \u2013 from \u2013 \u8868\u540d (1) \u2013 where \u7b5b\u9009\u6761\u4ef6 \u2013 order by \u6392\u5e8f\u5217\u8868 ASC | DESC<\/p>\n

\u2013 （1）ASC:\u4ee3\u8868\u5347\u5e8f；DESC\u4ee3\u8868\u964d\u5e8f，\u5982\u679c\u4e0d\u5199，\u9ed8\u8ba4\u5347\u5e8f\u3002 \u2013 （2）order by \u5b50\u53e5\u4e2d\u53ef\u4ee5\u652f\u6301\u5355\u4e2a\u5b57\u6bb5\u3001\u591a\u4e2a\u5b57\u6bb5\u3001\u8868\u8fbe\u5f0f\u3001\u51fd\u6570\u3001\u522b\u540d \u2013 （3）order by \u5b50\u53e5\u4e00\u822c\u662f\u653e\u5728\u67e5\u8be2\u8bed\u53e5\u7684\u6700\u540e\u9762，\u4f46\u662flimit\u5b50\u53e5\u9664\u5916\u3002]<\/p>\n

\/*
\nselect
\n \u67e5\u8be2\u5217\u8868 （3）
\nfrom
\n \u8868\u540d （1）
\n[where \u7b5b\u9009\u6761\u4ef6] （2）
\norder by
\n \u6392\u5e8f\u5217\u8868 [asc | desc] （4）
\n \u7279\u70b9：
\n1\u3001asc\u4ee3\u8868\u7684\u662f\u5347\u5e8f，desc\u4ee3\u8868\u7684\u662f\u964d\u5e8f，\u5982\u679c\u4e0d\u5199，\u9ed8\u8ba4\u662f\u5347\u5e8f\u3002
\n2\u3001order by \u5b50\u53e5\u4e2d\u53ef\u4ee5\u652f\u6301\u5355\u4e2a\u5b57\u6bb5\u3001\u591a\u4e2a\u5b57\u6bb5\u3001\u8868\u8fbe\u5f0f\u3001\u51fd\u6570\u3001\u522b\u540d
\n3\u3001order by \u5b50\u53e5\u4e00\u822c\u662f\u653e\u5728\u67e5\u8be2\u8bed\u53e5\u7684\u6700\u540e\u9762，limit\u5b50\u53e5\u9664\u5916
\n*\/<\/span>
\n# eg:\u67e5\u8be2\u5458\u5de5\u4fe1\u606f，\u8981\u6c42\u5de5\u8d44\u4ece\u9ad8\u5230\u5e95\u6392\u5e8f<\/span>
\nSELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n employees
\nORDER<\/span> BY<\/span>
\n salary desc<\/span>;<\/span>
\n# eg：\u6309\u5e74\u85aa\u7684\u9ad8\u4f4e\u663e\u793a\u5458\u5de5\u7684\u4fe1\u606f\u548c\u5e74\u85aa（\u6309\u8868\u8fbe\u5f0f\u6392\u5e8f）<\/span>
\nSELECT<\/span>
\n *<\/span>,<\/span>
\n salary *<\/span> 12<\/span> *<\/span> (<\/span>1<\/span> +<\/span> ifnull(<\/span>commission_pct,<\/span>0<\/span>)<\/span>)<\/span> AS<\/span> \u5e74\u85aa
\nFROM<\/span>
\n employees
\nORDER<\/span> BY<\/span>
\n salary *<\/span> 12<\/span> *<\/span> (<\/span>1<\/span> +<\/span> ifnull(<\/span>commission_pct,<\/span>0<\/span>)<\/span>)<\/span> desc<\/span>;<\/span>
\n # eg:\u6309\u5e74\u85aa\u7684\u9ad8\u4f4e\u663e\u793a\u5458\u5de5\u7684\u4fe1\u606f\u548c\u5e74\u85aa（\u6309\u522b\u540d\u6392\u5e8f）<\/span>
\nSELECT<\/span>
\n *<\/span>,<\/span>
\n salary *<\/span> 12<\/span> *<\/span> (<\/span>1<\/span> +<\/span> ifnull(<\/span>commission_pct,<\/span>0<\/span>)<\/span>)<\/span> AS<\/span> \u5e74\u85aa
\nFROM<\/span>
\n employees
\nORDER<\/span> BY<\/span>
\n \u5e74\u85aa desc<\/span>;<\/span>
\n# eg:\u6309\u59d3\u540d\u7684\u957f\u5ea6\u663e\u793a\u5458\u5de5\u7684\u59d3\u540d\u548c\u5de5\u8d44（\u6309\u51fd\u6570\u6392\u5e8f）<\/span>
\n# concat() \u5b57\u7b26\u4e32\u7684\u62fc\u63a5<\/span>
\n# length() \u83b7\u53d6\u5b57\u7b26\u4e32\u7684\u957f\u5ea6<\/span>
\nSELECT<\/span>
\n length(<\/span>concat(<\/span>last_name,<\/span>first_name)<\/span>)<\/span> AS<\/span> \u59d3\u540d\u957f\u5ea6,<\/span>
\n concat(<\/span>last_name,<\/span>first_name)<\/span> AS<\/span> \u59d3\u540d,<\/span>
\n salary
\nFROM<\/span>
\n employees
\nORDER<\/span> BY<\/span>
\n length(<\/span>concat(<\/span>last_name,<\/span>first_name)<\/span>)<\/span> desc<\/span>;<\/span>
\n# eg:\u67e5\u8be2\u5458\u5de5\u4fe1\u606f，\u8981\u6c42\u5148\u6309\u5de5\u8d44\u5347\u5e8f，\u518d\u6309\u5458\u5de5\u7f16\u53f7\u964d\u5e8f（\u6309\u591a\u4e2a\u5b57\u6bb5\u6392\u5e8f）<\/span>
\nSELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n employees
\nORDER<\/span> BY<\/span>
\n salary asc<\/span>,<\/span>employee_id DESC<\/span>;<\/span><\/p>\n

4，\u5e38\u89c1\u51fd\u6570 [– \u51fd\u6570：\u5c06\u4e00\u7ec4\u903b\u8f91\u8bed\u53e5\u5c01\u88c5\u5728\u65b9\u6cd5\u4e2d，\u5bf9\u5916\u66b4\u9732\u65b9\u6cd5\u540d\u3002 \u7c7b\u6bd4\u4e8epython\u4e2d\u7684\u65b9\u6cd5 \u2013 \u51fd\u6570\u597d\u5904：\u9690\u85cf\u4e86\u7ec6\u8282；\u63d0\u9ad8\u4ee3\u7801\u7684\u91cd\u7528\u6027\u3002 \u2013 \u51fd\u6570\u8c03\u7528\u8bed\u6cd5\u683c\u5f0f： \u2013 select \u51fd\u6570\u540d(\u5b9e\u53c2\u5217\u8868) [from \u8868\u540d] \u2013 \u51fd\u6570\u7279\u70b9：\u53eb\u4ec0\u4e48（\u51fd\u6570\u540d\u79f0）；\u5e72\u4ec0\u4e48（\u51fd\u6570\u529f\u80fd） \u2013 \u51fd\u6570\u7684\u5206\u7c7b：\u5355\u884c\u51fd\u6570；\u5206\u7ec4\u51fd\u6570<\/p>\n

\u2013 \u5355\u884c\u51fd\u6570：\u5b57\u7b26\u51fd\u6570\u3001\u6570\u503c\u51fd\u6570\u3001\u65e5\u671f\u51fd\u6570\u3001\u5176\u4ed6\u51fd\u6570\u3001\u6d41\u7a0b\u63a7\u5236\u51fd\u6570-if \u3001\u6d41\u7a0b\u63a7\u5236\u51fd\u6570-case\u7ed3\u6784\u2026]<\/p>\n

\/*
\n\u5206\u7c7b：
\n1\u3001\u5355\u884c\u51fd\u6570
\n\u5982：concat\u3001ifnull\u3001length
\n\u5305\u542b：\u5b57\u7b26\u51fd\u6570\u3001\u6570\u5b66\u51fd\u6570\u3001\u65e5\u671f\u51fd\u6570\u3001\u5176\u4ed6\u51fd\u6570\u3001\u6d41\u7a0b\u63a7\u5236\u51fd\u6570-if\u51fd\u6570\u3001\u6d41\u7a0b\u63a7\u5236\u51fd\u6570-case\u7ed3\u6784
\n2\u3001\u5206\u7ec4\u51fd\u6570
\n\u529f\u80fd：\u505a\u7edf\u8ba1\u4f7f\u7528\u53c8\u79f0\u7edf\u8ba1\u51fd\u6570（\u805a\u5408\u51fd\u6570\u3001\u7ec4\u51fd\u6570）\u3002
\n*\/<\/span>
\n— \u67e5\u770bmysql\u9ed8\u8ba4\u7f16\u7801\u683c\u5f0f：<\/span>
\nshow<\/span> variables like<\/span> '%char%'<\/span>;<\/span>
\n— ********************************\u5b57\u7b26\u51fd\u6570*************************************<\/span>
\n— 1\u3001length :\u83b7\u53d6\u53c2\u6570\u503c\u7684\u5b57\u8282\u4e2a\u6570<\/span>
\n# \u6ce8\u610f：\u5bf9\u4e8e\u975eASCII\u5b57\u7b26（\u5982\u6c49\u5b57）,length\u8fd4\u56de\u7684\u4e0d\u662f\u5b57\u7b26\u7684\u4e2a\u6570，\u800c\u662f\u5b57\u7b26\u4e32\u7684\u5b57\u8282\u6570<\/span>
\nSELECT<\/span> LENGTH(<\/span>'hello'<\/span>)<\/span>;<\/span>
\nSELECT<\/span> LENGTH(<\/span>'\u4f60\u597dhello'<\/span>)<\/span>;<\/span>–\u6c49\u5b57\u4e00\u4e2a\u5b57，\u4e09\u4e2a\u5b57\u7b26<\/span>
\n— 2\u3001concat ：\u62fc\u63a5\u5b57\u7b26\u4e32<\/span>
\n# concat\u51fd\u6570\u7528\u4e8e\u5c06\u4e24\u4e2a\u6216\u591a\u4e2a\u5b57\u7b26\u4e32\u8fde\u63a5\u6210\u4e00\u4e2a\u5b57\u7b26\u4e32，\u53ef\u4ee5\u8fde\u63a5\u4efb\u610f\u6570\u91cf\u7684\u5b57\u7b26\u4e32\u5e76\u8fd4\u56de\u4e00\u4e2a\u7ec4\u5408\u540e\u7684\u5b57\u7b26\u4e32<\/span>
\n# concat_ws:\u7528\u4e8e\u6307\u5b9a\u5206\u9694\u7b26\u8fde\u63a5\u5b57\u7b26\u4e32\u3002<\/span>
\nSELECT<\/span> CONCAT(<\/span>'hello'<\/span>,<\/span>'world'<\/span>)<\/span> AS<\/span> out_put;<\/span>
\nSELECT<\/span> CONCAT_WS(<\/span>'-'<\/span>,<\/span>'hello'<\/span>,<\/span>'world'<\/span>)<\/span>;<\/span>–\u7ed3\u679c\u4e3a：hello-world<\/span>
\nSELECT<\/span> CONCAT(<\/span>last_name,<\/span>'_'<\/span>,<\/span>first_name)<\/span> AS<\/span> `<\/span>name`<\/span><\/span> FROM<\/span> employees;<\/span>–CONCAT\u7684\u65f6\u5019\u6ce8\u610f\u2018-\u2019\u7684\u4f4d\u7f6e<\/span>
\n— 3\u3001upper\u3001lower<\/span>
\n# upper ：\u7528\u4e8e\u5c06\u5b57\u7b26\u4e32\u8f6c\u6362\u6210\u5927\u5199<\/span>
\n# UPPER(str)<\/span>
\n# lower ：\u7528\u4e8e\u5c06\u5b57\u7b26\u4e32\u8f6c\u6362\u6210\u5c0f\u5199<\/span>
\n# LOWER(str)<\/span>
\nselect<\/span> UPPER(<\/span>'hello'<\/span>)<\/span>;<\/span>
\nSELECT<\/span> LOWER(<\/span>'HELLO'<\/span>)<\/span>;<\/span>
\n# eg: \u5c06\u59d3\u9996\u5b57\u6bcd\u5927\u5199，\u5176\u4ed6\u6240\u6709\u5b57\u6bcd\u90fd\u5c0f\u5199\u3002<\/span>
\n–SUBSTR(\u5b57\u6bb5, start, length)：\u622a\u53d6\u5b57\u7b26\u4e32，MySQL\u4e0b\u6807\u4ece 1 \u5f00\u59cb<\/span>
\nselect<\/span>
\nconcat_ws(<\/span>'-'<\/span>,<\/span>upper(<\/span>substr(<\/span>last_name,<\/span>1<\/span>,<\/span>1<\/span>)<\/span>)<\/span>,<\/span>lower(<\/span>substr(<\/span>last_name,<\/span>2<\/span>)<\/span>)<\/span>,<\/span>lower(<\/span>first_name)<\/span>)<\/span>
\nfrom<\/span>
\nemployees;<\/span>
\n— 4\u3001substr\u3001substring,\u4e24\u4e2a\u51fd\u6570\u5b8c\u5168\u7b49\u4ef7\u3002<\/span>
\n# substr ：\u7528\u4e8e\u4ece\u5b57\u7b26\u4e32\u4e2d\u63d0\u53d6\u5b50\u4e32\u3002<\/span>
\n # SUBSTR(str FROM pos FOR len)<\/span>
\n # str \u539f\u59cb\u5b57\u7b26\u4e32<\/span>
\n # pos \u662f\u5b50\u4e32\u7684\u8d77\u59cb\u4f4d\u7f6e（\u4ece1\u5f00\u59cb）<\/span>
\n # len \u8981\u63d0\u53d6\u5b50\u4e32\u7684\u957f\u5ea6（\u53ef\u9009）<\/span>
\n# substring ：\u7528\u4e8e\u4ece\u5b57\u7b26\u4e32\u4e2d\u63d0\u53d6\u5b50\u4e32\u3002<\/span>
\n # SUBSTRING(str FROM pos FOR len)<\/span>
\n # str \u539f\u59cb\u5b57\u7b26\u4e32<\/span>
\n # pos \u662f\u5b50\u4e32\u7684\u8d77\u59cb\u4f4d\u7f6e（\u4ece1\u5f00\u59cb）<\/span>
\n # len \u8981\u63d0\u53d6\u5b50\u4e32\u7684\u957f\u5ea6（\u53ef\u9009）<\/span>
\n# **********substr**********<\/span>
\nSELECT<\/span> SUBSTR(<\/span>'\u6b22\u8fce\u6765\u5230\u5170\u667a\u6570\u52a0\u5b66\u9662'<\/span>,<\/span>5<\/span>)<\/span> AS<\/span> out_put;<\/span>
\n— 5\u3001instr ：\u8fd4\u56de\u5b57\u4e32\u7b2c\u4e00\u6b21\u51fa\u73b0\u7684\u7d22\u5f15，\u5982\u679c\u627e\u4e0d\u5230\u5219\u8fd4\u56de0<\/span>
\nselect<\/span> INSTR(<\/span>'\u6b22\u8fce\u6765\u5230\u5170\u667a\u6570\u52a0\u5b66\u9662'<\/span>,<\/span>'\u5b66\u9662'<\/span>)<\/span>;<\/span>–\u8fd4\u56de9<\/span>
\nselect<\/span> INSTR(<\/span>'\u6b22\u8fce\u6765\u5230\u5170\u667a\u6570\u52a0\u5b66\u9662'<\/span>,<\/span>'\u6570\u6a21'<\/span>)<\/span>;<\/span>–\u8fd4\u56de0<\/span>
\nselect<\/span> INSTR(<\/span>'\u6b22hhhh\u8fce\u6765\u5230HHHH\u5170\u667a\u6570\u52a0\u5b66\u9662'<\/span>,<\/span>'H'<\/span>)<\/span>;<\/span>–\u8fd4\u56de2<\/span>
\n# 8\u3001<\/span>
\n# TRIM()：\u5220\u9664\u524d\u5bfc\u7a7a\u683c\u548c\u5c3e\u968f\u7a7a\u683c<\/span>
\n# RTRIM()：\u5220\u9664\u5c3e\u968f\u7a7a\u683c<\/span>
\n# LTRIM()：\u5220\u9664\u524d\u5bfc\u7a7a\u683c<\/span>
\nselect<\/span> LENGTH(<\/span>TRIM(<\/span>' \u5170\u667a\u6570\u52a0\u5b66\u9662 '<\/span>)<\/span>)<\/span> AS<\/span> out_put;<\/span>–\u8fd4\u56de18<\/span>
\nselect<\/span> TRIM(<\/span>' \u5170\u667a\u6570\u52a0\u5b66\u9662 '<\/span>)<\/span> AS<\/span> out_put;<\/span>
\n–\u601d\u8003？"\u5170\u667a \u6570\u52a0 \u5b66\u9662" \u4e2d\u95f4\u7684\u7a7a\u683c\u5982\u4f55\u5220\u9664<\/span>
\n— \u628a\u5b57\u7b26\u4e32\u91cc\u6240\u6709\u7a7a\u683c，\u66ff\u6362\u6210\u7a7a\u5b57\u7b26\u4e32，\u5b9e\u73b0\u5220\u9664\u5168\u90e8\u7a7a\u683c<\/span>
\nSELECT<\/span> REPLACE<\/span>(<\/span>'\u5170\u667a \u6570\u52a0 \u5b66\u9662'<\/span>,<\/span>' '<\/span>,<\/span>''<\/span>)<\/span> AS<\/span> out_put;<\/span><\/p>\n

# 9\u3001LPAD(str,len,padstr):\u8fd4\u56de\u5b57\u7b26\u4e32\u53c2\u6570，\u5e76\u5728\u5de6\u4fa7\u586b\u5145\u6307\u5b9a\u7684\u5b57\u7b26\u4e32\u3002<\/span>
\nselect<\/span> lpad(<\/span>'\u6570\u52a0'<\/span>,<\/span>4<\/span>,<\/span>'*'<\/span>)<\/span> AS<\/span> output;<\/span>–\u8fd4\u56de**\u6570\u52a0<\/span>
\nselect<\/span> lpad(<\/span>'\u6570\u52a0'<\/span>,<\/span>6<\/span>,<\/span>'*'<\/span>)<\/span> AS<\/span> output;<\/span>–\u8fd4\u56de****\u6570\u52a0<\/span><\/p>\n

# 10\u3001RPAD(str,len,padstr):\u5c06\u5b57\u7b26\u4e32\u8ffd\u52a0\u6307\u5b9a\u6b21\u6570<\/span>
\nselect<\/span> rpad(<\/span>'\u6570\u52a0'<\/span>,<\/span>4<\/span>,<\/span>'*'<\/span>)<\/span> AS<\/span> output;<\/span>–\u8fd4\u56de\u6570\u52a0**<\/span>
\n –\u9a6c\u51ac\u6885 —> \u9a6c*\u6885 <\/span>
\nSELECT<\/span> CONCAT(<\/span>LEFT<\/span>(<\/span>'\u9a6c\u51ac\u6885'<\/span>,<\/span>1<\/span>)<\/span>,<\/span>'*'<\/span>,<\/span>RIGHT<\/span>(<\/span>'\u9a6c\u51ac\u6885'<\/span>,<\/span>1<\/span>)<\/span>)<\/span> AS<\/span> output;<\/span><\/p>\n

# 11\u3001REPLACE(str,from_str,to_str)：\u66ff\u6362\u6307\u5b9a\u5b57\u7b26\u4e32\u7684\u6240\u6709\u51fa\u73b0\u4f4d\u7f6e<\/span>
\nselect<\/span> replace<\/span>(<\/span>'\u6b22\u8fce\u6765\u5230\u5170\u667a\u6570\u52a0\u5b66\u9662'<\/span>,<\/span>'\u5b66\u9662'<\/span>,<\/span>'\u5927\u5b66'<\/span>)<\/span> AS<\/span> out_put;<\/span>–\u8fd4\u56de\u6b22\u8fce\u6765\u5230\u5170\u667a\u6570\u52a0\u5927\u5b66<\/span>
\n— ********************************\u6570\u5b66\u51fd\u6570*************************************<\/span>
\n# 1\u3001ROUND(X,D)：\u5c06\u53c2\u6570\u56db\u820d\u4e94\u5165X\u5230 D\u5c0f\u6570\u4f4d\u3002<\/span>
\nSELECT<\/span> ROUND<\/span>(<\/span>3.14<\/span>)<\/span>;<\/span>–\u8fd4\u56de3<\/span>
\nSELECT<\/span> ROUND<\/span>(<\/span>3.1415926<\/span>,<\/span>2<\/span>)<\/span> AS<\/span> out_put;<\/span>–\u8fd4\u56de3.14<\/span>
\nSELECT<\/span> ROUND<\/span>(<\/span>3.146<\/span>,<\/span>2<\/span>)<\/span> AS<\/span> out_put;<\/span>–\u8fd4\u56de3.15<\/span>
\n# 2\u3001CEIL()：\u8fd4\u56de\u4e0d\u5c0f\u4e8e\u67d0\u4e2a\u503c\u7684\u6700\u5c0f\u6574\u6570\u503c X\u3002\u5411\u4e0a\u53d6\u6574,\u8fd4\u56de\u5927\u4e8e\u6216\u7b49\u4e8e\u8be5\u6570\u503c\u7684\u6700\u5c0f\u6574\u6570<\/span>
\nSELECT<\/span> CEIL(<\/span>3.1415926<\/span>)<\/span>;<\/span> –\u8fd4\u56de4<\/span>
\nSELECT<\/span> CEIL(<\/span>–<\/span>3.1415926<\/span>)<\/span>;<\/span>–\u8fd4\u56de-3<\/span>
\n# 3\u3001FLOOR(X)：\u8fd4\u56de\u4e0d\u5927\u4e8e\u67d0\u4e2a\u7279\u5b9a\u503c\u7684\u6700\u5927\u6574\u6570\u503c X\u3002\u5411\u4e0b\u53d6\u6574，\u8fd4\u56de\u5c0f\u4e8e\u6216\u7b49\u4e8e\u8be5\u6570\u503c\u7684\u6700\u5927\u6574\u6570<\/span>
\nSELECT<\/span> FLOOR(<\/span>3.14<\/span>)<\/span>;<\/span>–\u8fd4\u56de3<\/span>
\nSELECT<\/span> FLOOR(<\/span>–<\/span>3.14<\/span>)<\/span>;<\/span>–\u8fd4\u56de-4<\/span>
\n# 4\u3001TRUNCATE(X,D)：\u7528\u4e8e\u5c06\u6570\u503c\u622a\u65ad\u5230\u6307\u5b9a\u7684\u5c0f\u6570\u4f4d\u6570，\u76f4\u63a5\u53bb\u6389\u591a\u4f59\u7684\u5c0f\u6570\u4f4d\u800c\u4e0d\u8fdb\u884c\u56db\u820d\u4e94\u5165<\/span>
\nSELECT<\/span> TRUNCATE<\/span>(<\/span>123.456<\/span>,<\/span>2<\/span>)<\/span>;<\/span>–\u8fd4\u56de123.45<\/span>
\nSELECT<\/span> TRUNCATE<\/span>(<\/span>123.456<\/span>,<\/span>0<\/span>)<\/span>;<\/span>–\u8fd4\u56de123<\/span>
\n# 5\u3001MOD(N,M)：\u200bN % MN MOD M \u7528\u4e8e\u8ba1\u7b97\u4e24\u4e2a\u6570\u4e4b\u95f4\u7684\u4f59\u6570（\u6a21\u8fd0\u7b97）<\/span>
\n# N:\u88ab\u9664\u6570<\/span>
\n# M:\u9664\u6570<\/span>
\n# \u8ba1\u7b97\u516c\u5f0f：N-（N\/M）*M<\/span>
\nSELECT<\/span> 10<\/span> %<\/span> 3<\/span>;<\/span>–\u8fd4\u56de1<\/span>
\nSELECT<\/span> MOD<\/span>(<\/span>10<\/span>,<\/span>3<\/span>)<\/span>;<\/span>–\u8fd4\u56de1<\/span>
\n— ********************************\u65e5\u671f\u51fd\u6570*************************************<\/span>
\n# \u65e5\u671f\u51fd\u6570<\/span>
\n# 1\u3001now():\u8fd4\u56de\u5f53\u524d\u65e5\u671f\u548c\u65f6\u95f4\u7684\u503c<\/span>
\n# YYYY-MM-DD HH:MM:SS<\/span>
\nSELECT<\/span> NOW<\/span>(<\/span>)<\/span>;<\/span> # 2026-09-02 16:10:31<\/span>
\n# 2\u3001CURDATE()：\u8fd4\u56de\u5f53\u524d\u65e5\u671f<\/span>
\nSELECT<\/span> CURDATE(<\/span>)<\/span>;<\/span> # 2026-09-02 YYYY-MM-DD<\/span>
\n# 3\u3001CURTIME()：\u8fd4\u56de\u5f53\u524d\u65f6\u95f4<\/span>
\nSELECT<\/span> CURTIME(<\/span>)<\/span>;<\/span> # 16:11:47 HH:MM:SS<\/span>
\n# \u53ef\u4ee5\u83b7\u53d6\u6307\u5b9a\u90e8\u5206\u7684\u65f6\u95f4：\u5e74\u3001\u6708\u3001\u65e5\u3001\u65f6\u3001\u5206\u3001\u79d2<\/span>
\n# 4\u3001YEAR()：\u8fd4\u56de\u5e74\u4efd<\/span>
\nSELECT<\/span> YEAR<\/span>(<\/span>NOW<\/span>(<\/span>)<\/span>)<\/span>;<\/span> –\u8fd4\u56de2026<\/span>
\nSELECT<\/span> YEAR<\/span>(<\/span>'2027-08-17'<\/span>)<\/span>;<\/span>–\u8fd4\u56de2027<\/span>
\n— eg:\u67e5\u770b\u5458\u5de5\u8868\u4e2d\u5165\u804c\u65f6\u95f4\u7684\u5e74\u4efd\u4fe1\u606f<\/span>
\nSELECT<\/span> YEAR<\/span>(<\/span>hiredate)<\/span> FROM<\/span> employees;<\/span>
\n# 5\u3001MONTH()：\u8fd4\u56de\u8fc7\u53bb\u65e5\u671f\u4e4b\u540e\u7684\u6708\u4efd<\/span>
\nSELECT<\/span> MONTH<\/span>(<\/span>NOW<\/span>(<\/span>)<\/span>)<\/span> ;<\/span>–\u8fd4\u56de9<\/span>
\n# 6\u3001MONTHNAME()：\u8fd4\u56de\u6708\u4efd\u540d\u79f0<\/span>
\nSELECT<\/span> MONTHNAME(<\/span>NOW<\/span>(<\/span>)<\/span>)<\/span>;<\/span>–\u8fd4\u56deSeptember<\/span>
\n# 7\u3001DAY()：\u8fd4\u56de\u65e5<\/span>
\nSELECT<\/span> DAY<\/span>(<\/span>NOW<\/span>(<\/span>)<\/span>)<\/span>;<\/span>–\u8fd4\u56de2<\/span>
\n# 8\u3001HOUR()：\u63d0\u53d6\u5c0f\u65f6<\/span>
\nSELECT<\/span> HOUR<\/span>(<\/span>NOW<\/span>(<\/span>)<\/span>)<\/span>;<\/span>–\u8fd4\u56de16<\/span>
\n# 9\u3001MINUTE()：\u4ece\u53c2\u6570\u4e2d\u8fd4\u56de\u5206\u949f\u6570\u3002<\/span>
\nSELECT<\/span> MINUTE<\/span>(<\/span>NOW<\/span>(<\/span>)<\/span>)<\/span>;<\/span>–\u8fd4\u56de14<\/span>
\n# 10\u3001SECOND()：\u8fd4\u56de\u79d2<\/span>
\nSELECT<\/span> SECOND<\/span>(<\/span>NOW<\/span>(<\/span>)<\/span>)<\/span>;<\/span>–\u8fd4\u56de58<\/span>
\n# 11\u3001STR_TO_DATE(str,format)：\u5c06\u5b57\u7b26\u4e32\u8f6c\u6362\u4e3a\u65e5\u671f<\/span>
\n# str：\u8981\u8f6c\u6362\u7684\u65e5\u671f\u548c\u65f6\u95f4\u5b57\u7b26\u4e32<\/span>
\n# format：\u6307\u5b9a\u5b57\u7b26\u4e32\u7684\u683c\u5f0f<\/span>
\n\/*
\n\u683c\u5f0f\u5316\u7b26\u53f7：
\n%Y：\u56db\u4f4d\u6570\u5b57\u7684\u5e74\u4efd\u3002
\n%y：\u4e24\u4f4d\u6570\u5b57\u7684\u5e74\u4efd\u3002
\n%m：\u4e24\u4f4d\u6570\u5b57\u7684\u6708\u4efd（01 \u5230 12）\u3002
\n%c：\u6708\u4efd，\u6570\u503c（0 \u5230 12）\u3002
\n%d：\u4e24\u4f4d\u6570\u5b57\u7684\u65e5\u671f（00 \u5230 31）\u3002
\n%e：\u65e5\u671f，\u6570\u503c（0 \u5230 31）\u3002
\n%H：\u4e24\u4f4d\u6570\u5b57\u7684\u5c0f\u65f6，24 \u5c0f\u65f6\u5236（00 \u5230 23）\u3002
\n%h：\u4e24\u4f4d\u6570\u5b57\u7684\u5c0f\u65f6，12 \u5c0f\u65f6\u5236（01 \u5230 12）\u3002
\n%i：\u4e24\u4f4d\u6570\u5b57\u7684\u5206\u949f（00 \u5230 59）\u3002
\n%s：\u4e24\u4f4d\u6570\u5b57\u7684\u79d2（00 \u5230 59）\u3002
\n%p：AM \u6216 PM
\n*\/<\/span>
\nSELECT<\/span> STR_TO_DATE(<\/span>'2026-08-17'<\/span>,<\/span>'%Y-%m-%d'<\/span>)<\/span> AS<\/span> out_put;<\/span>–\u8fd4\u56de2026-08-17<\/span>
\n# eg:\u67e5\u8be2\u5165\u804c\u65e5\u671f\u4e3a：1992-04-03\u7684\u5458\u5de5\u4fe1\u606f<\/span>
\nSELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n hiredate =<\/span> '1992-04-03'<\/span>;<\/span><\/p>\n

SELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n hiredate =<\/span> STR_TO_DATE(<\/span>'4-3 1992'<\/span>,<\/span>'%c-%d %Y'<\/span>)<\/span>;<\/span>
\n# 12\u3001DATE_FORMAT(date,format)：\u5c06\u65e5\u671f\u6216\u65e5\u671f\u65f6\u95f4\u503c\u683c\u5f0f\u5316\u4e3a\u6307\u5b9a\u7684\u5b57\u7b26\u4e32\u683c\u5f0f<\/span>
\n# date：\u8981\u683c\u5f0f\u5316\u7684\u65e5\u671f\u6216\u8005\u65e5\u671f\u65f6\u95f4<\/span>
\n# format：\u6307\u5b9a\u7ed3\u679c\u5b57\u7b26\u4e32\u7684\u683c\u5f0f<\/span>
\n\/*
\n\u683c\u5f0f\u5316\u7b26\u53f7：
\n%Y：\u56db\u4f4d\u6570\u5b57\u7684\u5e74\u4efd\u3002
\n%y：\u4e24\u4f4d\u6570\u5b57\u7684\u5e74\u4efd\u3002
\n%M：\u6708\u4efd\u540d\u79f0（January \u5230 December）\u3002
\n%m：\u4e24\u4f4d\u6570\u5b57\u7684\u6708\u4efd（01 \u5230 12）\u3002
\n%c：\u6708\u4efd，\u6570\u503c（1 \u5230 12）\u3002
\n%D：\u5e26\u6709\u82f1\u6587\u5e8f\u6570\u540e\u7f00\u7684\u6708\u4efd\u4e2d\u7684\u5929（1st, 2nd, 3rd, \u2026）\u3002
\n%d：\u4e24\u4f4d\u6570\u5b57\u7684\u65e5\u671f（00 \u5230 31）\u3002
\n%e：\u65e5\u671f，\u6570\u503c（0 \u5230 31）\u3002
\n%H：\u4e24\u4f4d\u6570\u5b57\u7684\u5c0f\u65f6，24 \u5c0f\u65f6\u5236（00 \u5230 23）\u3002
\n%h：\u4e24\u4f4d\u6570\u5b57\u7684\u5c0f\u65f6，12 \u5c0f\u65f6\u5236（01 \u5230 12）\u3002
\n%i：\u4e24\u4f4d\u6570\u5b57\u7684\u5206\u949f（00 \u5230 59）\u3002
\n%s：\u4e24\u4f4d\u6570\u5b57\u7684\u79d2（00 \u5230 59）\u3002
\n%p：AM \u6216 PM\u3002
\n%W：\u661f\u671f\u540d\u79f0（Sunday \u5230 Saturday）\u3002
\n%w：\u661f\u671f\u4e2d\u7684\u5929（0 = Sunday, 6 = Saturday）\u3002
\n%j：\u4e00\u5e74\u4e2d\u7684\u5929\u6570（001 \u5230 366）\u3002
\n*\/<\/span>
\nselect<\/span> DATE_FORMAT(<\/span>NOW<\/span>(<\/span>)<\/span>,<\/span>'%y\u5e74%m\u6708%d\u65e5'<\/span>)<\/span>;<\/span>–\u8fd4\u56de26\u5e7409\u670802\u65e5<\/span>
\n# eg:\u67e5\u8be2\u6709\u5956\u91d1\u7387\u7684\u5458\u5de5\u540d\u548c\u5165\u804c\u65e5\u671f（xx\u6708\/xx\u65e5 xx\u5e74）<\/span>
\nSELECT<\/span>
\n first_name,<\/span>
\n DATE_FORMAT(<\/span>hiredate,<\/span>'%m\u6708\/%d\u65e5 %y\u5e74'<\/span>)<\/span>
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n commission_pct is<\/span> not<\/span> null<\/span>;<\/span>
\n — ********************************\u6d41\u7a0b\u63a7\u5236\u51fd\u6570*************************************<\/span>
\n # \u6d41\u7a0b\u63a7\u5236\u51fd\u6570<\/span>
\n# 1\u3001IF(expr1,expr2,expr3)：\u7528\u4e8e\u67e5\u8be2\u4e2d\u8fdb\u884c\u6761\u4ef6\u5224\u65ad\u7684\u6d41\u7a0b\u63a7\u5236\u51fd\u6570<\/span>
\n# expr1：\u8981\u5224\u65ad\u7684\u6761\u4ef6\u8868\u8fbe\u5f0f，\u5982\u679c\u6761\u4ef6\u4e3a\u771f（\u975e\u96f6\u6216\u975e\u7a7a），\u5219\u8fd4\u56deexpr2，\u5426\u5219\u8fd4\u56deexpr3<\/span>
\n# expr2：\u6761\u4ef6\u4e3a\u771f\u65f6\u8fd4\u56de\u7684\u503c<\/span>
\n# expr3：\u6761\u4ef6\u4e3a\u5047\u65f6\u8fd4\u56de\u7684\u503c<\/span>
\nSELECT<\/span> IF<\/span>(<\/span>2<\/span> <<\/span> 3<\/span>,<\/span>'\u5927'<\/span>,<\/span>'\u5c0f'<\/span>)<\/span> AS<\/span> out_put;<\/span>–\u8fd4\u56de\u5c0f<\/span>
\n# eg:\u67e5\u8be2\u5458\u5de5\u7684\u59d3\u548c\u540d\u4ee5\u53ca\u5956\u91d1\u7387，\u5982\u679c\u6709\u5956\u91d1\u7387\u5219\u8fd4\u56de\u6709，\u6ca1\u6709\u5219\u8fd4\u56de\u65e0\u5e76\u4ee5\u5907\u6ce8\u4e3a\u5217\u540d\u3002<\/span>
\n\/*
\n\u5206\u6790：
\n \u67e5\u8be2\u7684\u8868：employees
\n \u67e5\u8be2\u7684\u5b57\u6bb5：last_name first_name commission_pct \u5907\u6ce8
\n \u67e5\u8be2\u7684\u6761\u4ef6：\u65e0
\n \u6392\u5e8f\u7684\u6761\u4ef6：\u65e0
\n*\/<\/span>
\nSELECT<\/span>
\n last_name,<\/span>
\n first_name,<\/span>
\n commission_pct,<\/span>
\n IF<\/span>(<\/span>commission_pct IS<\/span> NULL<\/span>,<\/span>'\u65e0'<\/span>,<\/span>'\u6709'<\/span>)<\/span> AS<\/span> \u5907\u6ce8
\nFROM<\/span>
\n employees;<\/span>
\n# 2\u3001CASE：\u662f\u4e00\u79cd\u6d41\u7a0b\u63a7\u5236\u51fd\u6570，\u7c7b\u4f3c\u7f16\u7a0b\u8bed\u8a00\u4e2d\u7684switch\u8bed\u6cd5\u3002<\/span>
\n# \u8bed\u6cd5\u683c\u5f0f1：<\/span>
\n# CASE value WHEN compare_value THEN result [WHEN compare_value THEN result …] [ELSE result] END<\/span>
\n# value：\u9700\u8981\u8fdb\u884c\u6bd4\u8f83\u7684\u8868\u8fbe\u5f0f\u6216\u8005\u5217<\/span>
\n# compare_value：\u8fdb\u884c\u6bd4\u8f83\u7684\u8868\u8fbe\u5f0f\u6216\u503c<\/span>
\n# result：\u5f53value\u7b49\u4e8ecompare_value\u65f6\u8fd4\u56de\u7684\u7ed3\u679c<\/span>
\n# [ELSE result]：\u5982\u679c\u6ca1\u6709\u6761\u4ef6\u8868\u8fbe\u5f0f\u4e3a\u771f\u65f6，\u5219\u8fd4\u56de\u7684\u9ed8\u8ba4\u7ed3\u679c<\/span><\/p>\n

# \u8bed\u6cd5\u683c\u5f0f2：<\/span>
\n# CASE WHEN condition THEN result [WHEN condition THEN result …] [ELSE result] END<\/span>
\n# condition：\u6761\u4ef6\u8868\u8fbe\u5f0f，\u53ef\u4ee5\u65f6\u4efb\u4f55\u5e03\u5c14\u8868\u8fbe\u5f0f<\/span>
\n# result：\u5f53\u6761\u4ef6\u8868\u8fbe\u5f0f\u4e3a\u771f\u65f6\u8fd4\u56de\u7684\u7ed3\u679c<\/span>
\n# ELSE result：\u5982\u679c\u6ca1\u6709\u6761\u4ef6\u8868\u8fbe\u5f0f\u4e3a\u771f\u65f6，\u5219\u8fd4\u56de\u7684\u9ed8\u8ba4\u7ed3\u679c<\/span><\/p>\n

# eg:\u67e5\u8be2\u5458\u5de5\u7684\u5de5\u8d44，\u8981\u6c42\u5982\u4e0b：<\/span>
\n# （1）\u90e8\u95e8\u53f7=30，\u663e\u793a\u7684\u5de5\u8d44\u4e3a1.1\u500d<\/span>
\n# （2）\u90e8\u95e8\u53f7=40，\u663e\u793a\u7684\u5de5\u8d44\u4e3a1.2\u500d<\/span>
\n# （3）\u90e8\u95e8\u53f7=50，\u663e\u793a\u7684\u5de5\u8d44\u4e3a1.3\u500d<\/span>
\n# （4）\u5176\u4ed6\u90e8\u95e8，\u663e\u793a\u7684\u5de5\u8d44\u4e3a\u539f\u5de5\u8d44<\/span>
\n\/*
\n\u5206\u6790：
\n \u67e5\u8be2\u7684\u8868：employees
\n \u67e5\u8be2\u7684\u5b57\u6bb5：salary department_id \u65b0\u5de5\u8d44
\n \u67e5\u8be2\u7684\u6761\u4ef6：\u65e0
\n \u6392\u5e8f\u7684\u6761\u4ef6：\u65e0
\n*\/<\/span>
\n# \u8bed\u6cd5\u683c\u5f0f1：<\/span>
\nSELECT<\/span>
\n salary,<\/span>
\n department_id,<\/span>
\n CASE<\/span>
\n department_id
\n WHEN<\/span> 30<\/span> THEN<\/span>
\n salary *<\/span> 1.1<\/span>
\n WHEN<\/span> 40<\/span> THEN<\/span>
\n salary *<\/span> 1.2<\/span>
\n WHEN<\/span> 50<\/span> THEN<\/span>
\n salary *<\/span> 1.3<\/span> ELSE<\/span> salary
\n END<\/span> AS<\/span> \u65b0\u5de5\u8d44
\nFROM<\/span>
\n employees;<\/span>
\n# \u4f7f\u7528\u8bed\u6cd5\u683c\u5f0f2\u505a\u4e00\u904d\u3002<\/span>
\nSELECT<\/span>
\n salary,<\/span>
\n department_id,<\/span>
\n CASE<\/span>
\n WHEN<\/span> department_id=<\/span>30<\/span> THEN<\/span>
\n salary *<\/span> 1.1<\/span>
\n WHEN<\/span> department_id=<\/span>40<\/span> THEN<\/span>
\n salary *<\/span> 1.2<\/span>
\n WHEN<\/span> department_id=<\/span>50<\/span> THEN<\/span>
\n salary *<\/span> 1.3<\/span> ELSE<\/span> salary
\n END<\/span> AS<\/span> \u65b0\u5de5\u8d44
\nFROM<\/span>
\n employees;<\/span><\/p>\n

# eg:\u67e5\u8be2\u5458\u5de5\u7684\u5de5\u8d44\u60c5\u51b5：<\/span>
\n# （1）\u5982\u679c\u5de5\u8d44\u5927\u4e8e20000，\u663e\u793aA\u7ea7\u522b<\/span>
\n# （2）\u5982\u679c\u5de5\u8d44\u5927\u4e8e15000，\u663e\u793aB\u7ea7\u522b<\/span>
\n# （3）\u5982\u679c\u5de5\u8d44\u5927\u4e8e10000，\u663e\u793aC\u7ea7\u522b<\/span>
\n# （4）\u5426\u5219，\u663e\u793aD\u7ea7\u522b<\/span>
\nSELECT<\/span>
\n salary,<\/span>
\n CASE<\/span>
\n WHEN<\/span> salary ><\/span> 20000<\/span> THEN<\/span>
\n 'A'<\/span>
\n WHEN<\/span> salary ><\/span> 15000<\/span> THEN<\/span>
\n 'B'<\/span>
\n WHEN<\/span> salary ><\/span> 10000<\/span> THEN<\/span>
\n 'C'<\/span>
\n ELSE<\/span>
\n 'D'<\/span>
\n END<\/span> AS<\/span> \u5de5\u8d44\u7ea7\u522b
\nFROM<\/span>
\n employees;<\/span>
\n— ********************************\u5206\u7ec4\u51fd\u6570*************************************<\/span>
\n# \u5206\u7ec4\u51fd\u6570：\u7528\u4f5c\u7edf\u8ba1\u4f7f\u7528，\u53c8\u79f0\u4e3a\u805a\u5408\u51fd\u6570\u6216\u8005\u7edf\u8ba1\u51fd\u6570\u6216\u8005\u7ec4\u51fd\u6570<\/span>
\n# \u5206\u7ec4\u51fd\u6570：<\/span>
\n# max()：\u8fd4\u56de\u6700\u5927\u503c<\/span>
\n# min():\u8fd4\u56de\u6700\u5c0f\u503c<\/span>
\n# avg():\u8fd4\u56de\u53c2\u6570\u7684\u5e73\u5747\u503c<\/span>
\n# count():\u8fd4\u56de\u8fd4\u56de\u7684\u884c\u6570<\/span>
\n# sum():\u8fd4\u56de\u603b\u548c<\/span>
\n# \u603b\u7ed3：<\/span>
\n# sum\u3001avg\u4e00\u822c\u7528\u4e8e\u5904\u7406\u6570\u503c\u578b，max\u3001min\u3001count\u53ef\u4ee5\u5904\u7406\u4efb\u4f55\u7c7b\u578b<\/span>
\n# max\u3001min\u3001avg\u3001count\u3001sum\u805a\u5408\u51fd\u6570\u90fd\u5ffd\u7565null\u503c<\/span>
\n# \u53ef\u4ee5\u548cdistinct\u642d\u914d\u5b9e\u73b0\u53bb\u91cd\u7684\u8fd0\u7b97<\/span>
\n# \u4e00\u822c\u4f7f\u7528count(*)\u505a\u7edf\u8ba1\u51fd\u6570<\/span>
\n# \u548c\u805a\u5408\u51fd\u6570\u4e00\u540c\u67e5\u8be2\u7684\u5b57\u6bb5\u8981\u6c42\u662f group by \u5173\u952e\u5b57\u540e\u9762\u7684\u5b57\u6bb5<\/span>
\n# 1\u3001sum()<\/span>
\nSELECT<\/span>
\n SUM<\/span>(<\/span>salary)<\/span> AS<\/span> sum_sal
\nFROM<\/span>
\n employees;<\/span>
\n# 2\u3001avg()<\/span>
\nSELECT<\/span>
\n ROUND<\/span>(<\/span>AVG<\/span>(<\/span> salary )<\/span>,<\/span>2<\/span>)<\/span> AS<\/span> avg_sal
\nFROM<\/span>
\n employees;<\/span>
\n# 3\u3001max()<\/span>
\nSELECT<\/span>
\n MAX<\/span>(<\/span> salary )<\/span> AS<\/span> max_sal
\nFROM<\/span>
\n employees;<\/span>
\n# 4\u3001min()<\/span>
\nSELECT<\/span> min<\/span>(<\/span>salary)<\/span> AS<\/span> min_sal from<\/span> employees;<\/span>
\n# 5\u3001count()<\/span>
\nSELECT<\/span> COUNT<\/span>(<\/span>salary)<\/span> as<\/span> count_sal FROM<\/span> employees;<\/span>
\nSELECT<\/span> COUNT<\/span>(<\/span>commission_pct)<\/span> as<\/span> count_sal FROM<\/span> employees;<\/span> # \u5ffd\u7565null\u503c<\/span><\/p>\n

# \u603b\u7ed3<\/span>
\n# *****************\u5904\u7406\u6570\u503c\u578b*****************<\/span>
\nSELECT<\/span> SUM<\/span>(<\/span>last_name)<\/span>,<\/span>AVG<\/span>(<\/span>last_name)<\/span> FROM<\/span> employees;<\/span> # sum\u3001avg\u4e0d\u5efa\u8bae\u7528\u5904\u7406\u5b57\u7b26\u578b<\/span><\/p>\n

SELECT<\/span> SUM<\/span>(<\/span>hiredate)<\/span>,<\/span>AVG<\/span>(<\/span>hiredate)<\/span> FROM<\/span> employees;<\/span> # sum\u3001avg\u4e0d\u5efa\u8bae\u7528\u5904\u7406\u65e5\u671f\u578b<\/span><\/p>\n

SELECT<\/span> MAX<\/span>(<\/span>last_name)<\/span>,<\/span>MIN<\/span>(<\/span>last_name)<\/span> FROM<\/span> employees;<\/span> # max\u3001min\u9002\u5408\u5904\u7406\u4efb\u4f55\u7c7b\u578b<\/span><\/p>\n

SELECT<\/span> MAX<\/span>(<\/span>hiredate)<\/span>,<\/span>MIN<\/span>(<\/span>hiredate)<\/span> FROM<\/span> employees;<\/span> # max\u3001min\u9002\u5408\u5904\u7406\u4efb\u4f55\u7c7b\u578b<\/span><\/p>\n

SELECT<\/span> COUNT<\/span>(<\/span>commission_pct)<\/span> FROM<\/span> employees;<\/span> # count \u5ffd\u7565null\u503c<\/span><\/p>\n

SELECT<\/span> COUNT<\/span>(<\/span>last_name)<\/span> FROM<\/span> employees;<\/span> # count\u9002\u5408\u5904\u7406\u4efb\u4f55\u7c7b\u578b<\/span>
\n# \u662f\u5426\u5ffd\u7565null\u503c<\/span>
\nSELECT<\/span> SUM<\/span>(<\/span>commission_pct)<\/span>,<\/span>AVG<\/span>(<\/span>commission_pct)<\/span>,<\/span>SUM<\/span>(<\/span>commission_pct)<\/span> \/<\/span> 35<\/span>,<\/span>SUM<\/span>(<\/span>commission_pct)<\/span> \/<\/span> 107<\/span> FROM<\/span> employees;<\/span>–\u5ffd\u7565null<\/span><\/p>\n

SELECT<\/span> MAX<\/span>(<\/span>commission_pct)<\/span>,<\/span>MIN<\/span>(<\/span>commission_pct)<\/span> FROM<\/span> employees;<\/span><\/p>\n

SELECT<\/span> COUNT<\/span>(<\/span>commission_pct)<\/span> FROM<\/span> employees;<\/span> # count \u5ffd\u7565null\u503c<\/span><\/p>\n

SELECT<\/span> COUNT<\/span>(<\/span>last_name)<\/span> FROM<\/span> employees;<\/span>
\n# \u642d\u914ddistinct\u5b9e\u73b0\u53bb\u91cd<\/span>
\n# max min<\/span>
\nSELECT<\/span> max<\/span>(<\/span>distinct<\/span> salary)<\/span>,<\/span>min<\/span>(<\/span>salary)<\/span> FROM<\/span> employees;<\/span>
\nSELECT<\/span> SUM<\/span>(<\/span>distinct<\/span> salary)<\/span>,<\/span>SUM<\/span>(<\/span>salary)<\/span> FROM<\/span> employees;<\/span>
\n# count<\/span>
\nSELECT<\/span> COUNT<\/span>(<\/span>DISTINCT<\/span> salary)<\/span>,<\/span>COUNT<\/span>(<\/span>salary)<\/span> FROM<\/span> employees;<\/span>
\n# count()\u8be6\u7ec6\u8bf4\u660e<\/span>
\nSELECT<\/span> COUNT<\/span>(<\/span>salary)<\/span> FROM<\/span> employees;<\/span>–\u5ffd\u7565 NULL<\/span>
\nSELECT<\/span> COUNT<\/span>(<\/span>*<\/span>)<\/span> FROM<\/span> employees;<\/span>–\u4e0d\u4f1a\u5ffd\u7565 NULL<\/span>
\nSELECT<\/span> COUNT<\/span>(<\/span>1<\/span>)<\/span> FROM<\/span> employees;<\/span>–\u4e0d\u4f1a\u5ffd\u7565 NULL<\/span><\/p>\n

(5)，\u5206\u7ec4\u67e5\u8be2 [– select \u2013 \u5206\u7ec4\u51fd\u6570, \u2013 \u5217\u540d（\u8981\u6c42\u51fa\u73b0\u5728group by\u540e\u9762）(5) \u2013 FROM \u2013 \u8868\u540d (1) \u2013 [where \u7b5b\u9009\u6761\u4ef6] (2) \u2013 group by \u2013 \u5206\u7ec4\u7684\u5217\u8868 (3) \u2013 having \u5b50\u53e5 (4) \u2013 [order by \u5b50\u53e5] (6)<\/p>\n

1\u3001\u5206\u7ec4\u67e5\u8be2\u4e2d\u7684\u7b5b\u9009\u6761\u4ef6\u5206\u4e3a\u4e24\u7c7b：<\/p>\n

\u5206\u7ec4\u524d\u7b5b\u9009 \u539f\u59cb\u8868 group by \u5b50\u53e5\u7684\u524d\u9762 where<\/p>\n

\u5206\u7ec4\u540e\u7b5b\u9009 \u5206\u7ec4\u540e\u7684\u7ed3\u679c\u96c6（\u865a\u8868） group by \u5b50\u53e5\u7684\u540e\u9762 having \u6ce8\u610f： （1）\u5206\u7ec4\u51fd\u6570\u505a\u6761\u4ef6\u80af\u5b9a\u662f\u653e\u5728having\u5b50\u53e5\u4e2d\u3002 （2）\u80fd\u7528\u5206\u7ec4\u524d\u7b5b\u9009\u7684，\u5c31\u6709\u9650\u8003\u8651\u4f7f\u7528\u5206\u7ec4\u524d\u7b5b\u9009\u3002 2\u3001group by \u5b50\u53e5\u652f\u6301\u5355\u5b57\u6bb5\u5206\u7ec4\u3001\u591a\u5b57\u6bb5\u5206\u7ec4（\u591a\u4e2a\u5b57\u6bb5\u4e4b\u95f4\u4f7f\u7528\u9017\u53f7\u9694\u5f00\u6ca1\u6709\u5148\u540e\u987a\u5e8f）\u3001\u8868\u8fbe\u5f0f\u6216\u8005\u51fd\u6570 3\u3001\u4e5f\u53ef\u4ee5\u6dfb\u52a0\u6392\u5e8f（\u6392\u5e8f\u653e\u5728\u6574\u4e2a\u5206\u7ec4\u67e5\u8be2\u7684\u6700\u540e）]<\/p>\n

— \u5206\u7ec4\u67e5\u8be2\u8bed\u6cd5\u603b\u7ed3：<\/span>
\n— select <\/span>
\n— \u5206\u7ec4\u51fd\u6570,<\/span>
\n— \u5217\u540d（\u8981\u6c42\u51fa\u73b0\u5728group by\u540e\u9762）(5)<\/span>
\n— FROM<\/span>
\n— \u8868\u540d (1)<\/span>
\n— [where \u7b5b\u9009\u6761\u4ef6] (2)<\/span>
\n— group by <\/span>
\n— \u5206\u7ec4\u7684\u5217\u8868 (3)<\/span>
\n— having \u5b50\u53e5 (4)<\/span>
\n— [order by \u5b50\u53e5] (6)<\/span><\/p>\n

*<\/span>*<\/span># 1\u3001\u5206\u7ec4\u67e5\u8be2\u4e2d\u7684\u7b5b\u9009\u6761\u4ef6\u5206\u4e3a\u4e24\u7c7b：<\/span><\/p>\n

# \u5206\u7ec4\u524d\u7b5b\u9009 \u539f\u59cb\u8868 group by \u5b50\u53e5\u7684\u524d\u9762 where<\/span><\/p>\n

# \u5206\u7ec4\u540e\u7b5b\u9009 \u5206\u7ec4\u540e\u7684\u7ed3\u679c\u96c6（\u865a\u8868） group by \u5b50\u53e5\u7684\u540e\u9762 having<\/span>
\n# \u6ce8\u610f：<\/span>
\n# （1）\u5206\u7ec4\u51fd\u6570\u505a\u6761\u4ef6\u80af\u5b9a\u662f\u653e\u5728having\u5b50\u53e5\u4e2d\u3002<\/span>
\n# （2）\u80fd\u7528\u5206\u7ec4\u524d\u7b5b\u9009\u7684，\u5c31\u6709\u9650\u8003\u8651\u4f7f\u7528\u5206\u7ec4\u524d\u7b5b\u9009\u3002<\/span>
\n# 2\u3001group by \u5b50\u53e5\u652f\u6301\u5355\u5b57\u6bb5\u5206\u7ec4\u3001\u591a\u5b57\u6bb5\u5206\u7ec4（\u591a\u4e2a\u5b57\u6bb5\u4e4b\u95f4\u4f7f\u7528\u9017\u53f7\u9694\u5f00\u6ca1\u6709\u5148\u540e\u987a\u5e8f）\u3001\u8868\u8fbe\u5f0f\u6216\u8005\u51fd\u6570<\/span>
\n# 3\u3001\u4e5f\u53ef\u4ee5\u6dfb\u52a0\u6392\u5e8f（\u6392\u5e8f\u653e\u5728\u6574\u4e2a\u5206\u7ec4\u67e5\u8be2\u7684\u6700\u540e）<\/span><\/p>\n

# eg:\u67e5\u8be2\u90ae\u7bb1\u4e2d\u5305\u542ba\u5b57\u7b26\u7684\u6bcf\u4e2a\u90e8\u95e8\u7684\u5e73\u5747\u5de5\u8d44\u3002<\/span>
\nSELECT<\/span>
\n AVG<\/span>(<\/span>salary)<\/span> as<\/span> avg_sal,<\/span>
\n department_id
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n email like<\/span> '%a%'<\/span>
\nGROUP<\/span> BY<\/span>
\n department_id;<\/span><\/p>\n

–eg:\u67e5\u8be2\u6709\u5956\u91d1\u7387\u7684\u6bcf\u4e2a\u9886\u5bfc\u624b\u4e0b\u5458\u5de5\u7684\u6700\u9ad8\u5de5\u8d44<\/span>
\n SELECT<\/span>
\n MAX<\/span>(<\/span>salary)<\/span> as<\/span> max_sal ,<\/span>
\n manager_id
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n commission_pct is<\/span> not<\/span> null<\/span>
\nGROUP<\/span> BY<\/span>
\n manager_id;<\/span><\/p>\n

–eg:\u67e5\u8be2\u54ea\u4e2a\u90e8\u95e8\u7684\u5458\u5de5\u4e2a\u6570\u5927\u4e8e2<\/span>
\nSELECT<\/span>
\n COUNT<\/span>(<\/span>*<\/span>)<\/span>,<\/span>
\n department_id
\nfrom<\/span>
\n employees
\nGROUP<\/span> BY<\/span>
\n department_id
\nHAVING<\/span>
\n COUNT<\/span>(<\/span>*<\/span>)<\/span> ><\/span> 2<\/span>;<\/span>
\n–\u5148\u5206\u7c7b\u540e\u7edf\u8ba1\u7528having<\/span><\/p>\n

#eg:\u67e5\u8be2\u6bcf\u4e2a\u5de5\u79cd\u6709\u5956\u91d1\u7387\u7684\u5458\u5de5\u7684\u6700\u9ad8\u5de5\u8d44\u5927\u4e8e12000\u7684\u5de5\u79cd\u7f16\u53f7\u548c\u6700\u9ad8\u5de5\u8d44<\/span>
\n# \u5206\u6790（1）：\u67e5\u8be2\u6bcf\u4e2a\u5de5\u79cd\u6709\u5956\u91d1\u7387\u7684\u5458\u5de5\u7684\u6700\u9ad8\u5de5\u8d44<\/span>
\nSELECT<\/span>
\n max<\/span>(<\/span>salary)<\/span> as<\/span> max_sal,<\/span>
\n job_id
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n commission_pct is<\/span> not<\/span> null<\/span>
\nGROUP<\/span> BY<\/span>
\n job_id;<\/span><\/p>\n

# \u5206\u6790（2）:\u6839\u636e(1)\u7684\u7ed3\u679c\u7ee7\u7eed\u7b5b\u9009，\u6700\u9ad8\u5de5\u8d44\u5927\u4e8e12000<\/span><\/p>\n

SELECT<\/span>
\n max<\/span>(<\/span>salary)<\/span> as<\/span> max_sal,<\/span>
\n job_id
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n commission_pct is<\/span> not<\/span> null<\/span>
\nGROUP<\/span> BY<\/span>
\n job_id
\nHAVING<\/span>
\n max_sal ><\/span> 12000<\/span>;<\/span>
\n# eg:\u67e5\u8be2\u9886\u5bfc\u7f16\u53f7\u5927\u4e8e102\u7684\u6bcf\u4e2a\u9886\u5bfc\u624b\u4e0b\u7684\u6700\u4f4e\u5de5\u8d44\u5927\u4e8e5000\u7684\u9886\u5bfc\u7f16\u53f7\u662f\u54ea\u4e2a，\u4ee5\u53ca\u5176\u6700\u4f4e\u5de5\u8d44\u3002<\/span>
\n# \u5206\u6790（1）：\u67e5\u8be2\u6bcf\u4e2a\u9886\u5bfc\u624b\u4e0b\u7684\u5458\u5de5\u56fa\u5b9a\u6700\u4f4e\u5de5\u8d44<\/span><\/p>\n

SELECT<\/span>
\n min<\/span>(<\/span>salary)<\/span>,<\/span>
\n manager_id
\nFROM<\/span>
\n employees
\nGROUP<\/span> BY<\/span>
\n manager_id;<\/span><\/p>\n

# \u5206\u6790（2）：\u6839\u636e（1）\u7684\u7ed3\u679c\u7ee7\u7eed\u6dfb\u52a0\u7b5b\u9009\u6761\u4ef6：\u7f16\u53f7\u5927\u4e8e102<\/span>
\nSELECT<\/span>
\n min<\/span>(<\/span>salary)<\/span>,<\/span>
\n manager_id
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n manager_id ><\/span> 102<\/span>
\nGROUP<\/span> BY<\/span>
\n manager_id;<\/span><\/p>\n

# \u5206\u6790（3）：\u6839\u636e（2）\u7684\u7ed3\u679c\u7ee7\u7eed\u7b5b\u9009，\u6700\u4f4e\u5de5\u8d44\u5927\u4e8e5000<\/span>
\nSELECT<\/span>
\n min<\/span>(<\/span>salary)<\/span>,<\/span>
\n manager_id
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n manager_id ><\/span> 102<\/span>
\nGROUP<\/span> BY<\/span>
\n manager_id
\nHAVING<\/span>
\n min<\/span>(<\/span>salary)<\/span> ><\/span> 5000<\/span>;<\/span>
\n# \u6309\u8868\u8fbe\u5f0f\u6216\u8005\u51fd\u6570\u5206\u7ec4<\/span>
\n# eg:\u6309\u5458\u5de5\u59d3\u540d\u7684\u957f\u5ea6\u5206\u7ec4，\u67e5\u8be2\u6bcf\u4e00\u7ec4\u7684\u5458\u5de5\u4e2a\u6570，\u7b5b\u9009\u5458\u5de5\u4e2a\u6570\u5927\u4e8e5\u7684\u6709\u54ea\u4e9b\u3002<\/span>
\n# \u5206\u6790（1）\u67e5\u8be2\u6bcf\u4e2a\u957f\u5ea6\u7684\u5458\u5de5\u4e2a\u6570<\/span>
\nSELECT<\/span>
\n COUNT<\/span>(<\/span>*<\/span>)<\/span>,<\/span>
\n LENGTH(<\/span>CONCAT(<\/span>last_name,<\/span>first_name)<\/span>)<\/span> AS<\/span> len_name
\nFROM<\/span>
\n employees
\nGROUP<\/span> BY<\/span>
\n LENGTH(<\/span>CONCAT(<\/span>last_name,<\/span>first_name)<\/span>)<\/span>
\n# \u5206\u6790（2）：\u6dfb\u52a0\u7b5b\u9009\u6761\u4ef6 \u5458\u5de5\u4e2a\u6570\u5927\u4e8e5<\/span>
\nSELECT<\/span>
\n COUNT<\/span>(<\/span>*<\/span>)<\/span>,<\/span>
\n LENGTH(<\/span>CONCAT(<\/span>last_name,<\/span>first_name)<\/span>)<\/span> AS<\/span> len_name
\nFROM<\/span>
\n employees
\nGROUP<\/span> BY<\/span>
\n LENGTH(<\/span>CONCAT(<\/span>last_name,<\/span>first_name)<\/span>)<\/span>
\nHAVING<\/span>
\n COUNT<\/span>(<\/span>*<\/span>)<\/span> ><\/span> 5<\/span>;<\/span><\/p>\n

# \u6309\u591a\u4e2a\u5b57\u6bb5\u5206\u7ec4<\/span>
\n# eg:\u67e5\u8be2\u6bcf\u4e2a\u90e8\u95e8\u6bcf\u4e2a\u5de5\u79cd\u7684\u5458\u5de5\u7684\u5e73\u5747\u5de5\u8d44<\/span>
\nSELECT<\/span>
\n AVG<\/span>(<\/span>salary)<\/span>,<\/span>
\n department_id,<\/span>
\n job_id
\nFROM<\/span>
\n employees
\nGROUP<\/span> BY<\/span>
\n department_id,<\/span>job_id;<\/span>
\n# \u6dfb\u52a0\u6392\u5e8f\u6761\u4ef6<\/span>
\n# eg:\u67e5\u8be2\u6bcf\u4e2a\u90e8\u95e8\u6bcf\u4e2a\u5de5\u79cd\u7684\u5e73\u5747\u5de5\u5de5\u8d44，\u5e76\u4e14\u6309\u5e73\u5747\u5de5\u8d44\u7684\u9ad8\u4f4e\u663e\u793a<\/span>
\nSELECT<\/span>
\n AVG<\/span>(<\/span>salary)<\/span>,<\/span>
\n department_id,<\/span>
\n job_id
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n department_id is<\/span> not<\/span> null<\/span>
\nGROUP<\/span> BY<\/span>
\n department_id,<\/span>job_id
\nHAVING<\/span>
\n AVG<\/span>(<\/span>salary)<\/span>><\/span> 10000<\/span>
\nORDER<\/span> BY<\/span>
\n AVG<\/span>(<\/span>salary)<\/span> DESC<\/span>;<\/span><\/p>\n

（6），\u8fde\u63a5\u67e5\u8be2 [ \u7b1b\u5361\u5c14\u79ef:\u662f\u4e24\u4e2a\u6216\u591a\u4e2a\u8868\u4e4b\u95f4\u7684\u8fde\u63a5\u64cd\u4f5c\u3002 \u7b1b\u5361\u5c14\u79ef\u73b0\u8c61：\u88681\u6709m\u884c，\u88682\u6709n\u884c，\u7ed3\u679c\u4e3a m * n \u7b1b\u5361\u513f\u79ef\u4ea7\u751f\u7684\u6761\u4ef6： 1\u3001\u7701\u7565\u8fde\u63a5\u6761\u4ef6 2\u3001\u8fde\u63a5\u6761\u4ef6\u65e0\u6548 3\u3001\u6240\u6709\u8868\u4e2d\u7684\u6240\u6709\u884c\u4e92\u76f8\u8fde\u63a5 \u6ce8\u610f：\u4e3a\u4e86\u907f\u514d\u7b1b\u5361\u5c14\u79ef\u4ea7\u751f\u53ef\u4ee5\u5728where\u5b50\u53e5\u540e\u9762\u52a0\u5165\u6709\u6548\u8fde\u63a5\u6761\u4ef6\u3002<\/p>\n

\u8fde\u63a5\u67e5\u8be2：\u53c8\u79f0\u4e3a\u591a\u8868\u67e5\u8be2，\u5f53\u67e5\u8be2\u7684\u5b57\u6bb5\u6765\u81ea\u591a\u4e2a\u8868\u65f6，\u5c31\u4f1a\u7528\u5230\u8fde\u63a5\u67e5\u8be2\u3002 \u8fde\u63a5\u67e5\u8be2\u5206\u7c7b： 1\u3001\u6309\u5e74\u4ee3\u5206\u7c7b： sql92\u6807\u51c6（\u6dd8\u6c70！！！，\u4e86\u89e3\u5373\u53ef） sql99\u6807\u51c6（\u63a8\u8350\u4f7f\u7528），\u652f\u6301\u5185\u8fde\u63a5 + \u5916\u8fde\u63a5（\u5de6\u5916\u3001\u53f3\u5916） + \u4ea4\u53c9\u8fde\u63a5 2\u3001\u6309\u529f\u80fd\u5206\u7c7b： （1）\u5185\u8fde\u63a5 a\u3001\u7b49\u503c\u8fde\u63a5 b\u3001\u975e\u7b49\u503c\u8fde\u63a5 c\u3001\u81ea\u8fde\u63a5 （2）\u5916\u8fde\u63a5 a\u3001\u5de6\u5916\u8fde\u63a5 b\u3001\u53f3\u5916\u8fde\u63a5 c\u3001\u5168\u5916\u8fde\u63a5 （3）\u4ea4\u53c9\u8fde\u63a5<\/p>\n

\u2013 \u8fde\u63a5\u67e5\u8be2\u8bed\u6cd5\u683c\u5f0f\u603b\u7ed3： \u2013 select (7) \u2013 \u67e5\u8be2\u5217\u8868 \u2013 from \u88681 \u522b\u540d [\u8fde\u63a5\u7c7b\u578b] (1) \u2013 join \u88682 \u522b\u540d (3) \u2013 on \u8fde\u63a5\u6761\u4ef6 (2) \u2013 [where \u7b5b\u9009\u6761\u4ef6] (4) \u2013 [group by \u5b50\u53e5] (5) \u2013 [having \u7b5b\u9009\u6761\u4ef6] (6) \u2013 [order by \u5b50\u53e5] (8)<\/p>\n

\u2013 \u8fde\u63a5\u6761\u4ef6\u5206\u7c7b： \u5185\u8fde\u63a5：INNER \u5916\u8fde\u63a5： \u5de6\u5916\u8fde\u63a5：LEFT [OUTER] \u53f3\u5916\u8fde\u63a5：RIGHT [OUTER] \u5168\u5916\u8fde\u63a5：full [OUTER] mysql\u4e0d\u652f\u6301\u5168\u5916！ \u4ea4\u53c9\u8fde\u63a5：CROSS]<\/p>\n

# \u9700\u6c42：\u67e5\u8be2\u6240\u6709\u5973\u660e\u661f\u5bf9\u5e94\u7684\u7537\u670b\u53cb\u3002<\/span>
\nSELECT<\/span> `<\/span>name`<\/span><\/span>,<\/span>boyname from<\/span> beauty,<\/span>boys;<\/span> — \u7b1b\u5361\u5c14\u79ef<\/span><\/p>\n

SELECT<\/span> `<\/span>name`<\/span><\/span>,<\/span>boyname from<\/span> beauty,<\/span>boys
\nWHERE<\/span> beauty.<\/span>boyfriend_id =<\/span> boys.<\/span>id;<\/span><\/p>\n

# \u7b1b\u5361\u5c14\u79ef:\u662f\u4e24\u4e2a\u6216\u591a\u4e2a\u8868\u4e4b\u95f4\u7684\u8fde\u63a5\u64cd\u4f5c\u3002<\/span>
\n# \u7b1b\u5361\u5c14\u79ef\u73b0\u8c61：\u88681\u6709m\u884c，\u88682\u6709n\u884c，\u7ed3\u679c\u4e3a m * n<\/span>
\n# \u7b1b\u5361\u513f\u79ef\u4ea7\u751f\u7684\u6761\u4ef6：<\/span>
\n# 1\u3001\u7701\u7565\u8fde\u63a5\u6761\u4ef6<\/span>
\n# 2\u3001\u8fde\u63a5\u6761\u4ef6\u65e0\u6548<\/span>
\n# 3\u3001\u6240\u6709\u8868\u4e2d\u7684\u6240\u6709\u884c\u4e92\u76f8\u8fde\u63a5<\/span>
\n# \u6ce8\u610f：\u4e3a\u4e86\u907f\u514d\u7b1b\u5361\u5c14\u79ef\u4ea7\u751f\u53ef\u4ee5\u5728where\u5b50\u53e5\u540e\u9762\u52a0\u5165\u6709\u6548\u8fde\u63a5\u6761\u4ef6\u3002<\/span><\/p>\n

# \u8fde\u63a5\u67e5\u8be2：\u53c8\u79f0\u4e3a\u591a\u8868\u67e5\u8be2，\u5f53\u67e5\u8be2\u7684\u5b57\u6bb5\u6765\u81ea\u591a\u4e2a\u8868\u65f6，\u5c31\u4f1a\u7528\u5230\u8fde\u63a5\u67e5\u8be2\u3002<\/span>
\n# \u8fde\u63a5\u67e5\u8be2\u5206\u7c7b：<\/span>
\n# 1\u3001\u6309\u5e74\u4ee3\u5206\u7c7b：<\/span>
\n# sql92\u6807\u51c6（\u6dd8\u6c70！！！，\u4e86\u89e3\u5373\u53ef）<\/span>
\n# sql99\u6807\u51c6（\u63a8\u8350\u4f7f\u7528），\u652f\u6301\u5185\u8fde\u63a5 + \u5916\u8fde\u63a5（\u5de6\u5916\u3001\u53f3\u5916） + \u4ea4\u53c9\u8fde\u63a5<\/span>
\n# 2\u3001\u6309\u529f\u80fd\u5206\u7c7b：<\/span>
\n# （1）\u5185\u8fde\u63a5<\/span>
\n# a\u3001\u7b49\u503c\u8fde\u63a5<\/span>
\n# b\u3001\u975e\u7b49\u503c\u8fde\u63a5<\/span>
\n# c\u3001\u81ea\u8fde\u63a5<\/span>
\n# （2）\u5916\u8fde\u63a5<\/span>
\n# a\u3001\u5de6\u5916\u8fde\u63a5<\/span>
\n# b\u3001\u53f3\u5916\u8fde\u63a5<\/span>
\n# c\u3001\u5168\u5916\u8fde\u63a5<\/span>
\n# （3）\u4ea4\u53c9\u8fde\u63a5<\/span><\/p>\n

— \u8fde\u63a5\u67e5\u8be2\u8bed\u6cd5\u683c\u5f0f\u603b\u7ed3：<\/span>
\n— select (7)<\/span>
\n— \u67e5\u8be2\u5217\u8868<\/span>
\n— from \u88681 \u522b\u540d [\u8fde\u63a5\u7c7b\u578b] (1)<\/span>
\n— join \u88682 \u522b\u540d (3)<\/span>
\n— on \u8fde\u63a5\u6761\u4ef6 (2)<\/span>
\n— [where \u7b5b\u9009\u6761\u4ef6](4)<\/span>
\n— [group by \u5b50\u53e5](5)<\/span>
\n— [having \u7b5b\u9009\u6761\u4ef6](6)<\/span>
\n— [order by \u5b50\u53e5](8)<\/span><\/p>\n

— \u8fde\u63a5\u6761\u4ef6\u5206\u7c7b：<\/span>
\n# \u5185\u8fde\u63a5：INNER<\/span>
\n# \u5916\u8fde\u63a5：<\/span>
\n# \u5de6\u5916\u8fde\u63a5：LEFT [OUTER]<\/span>
\n# \u53f3\u5916\u8fde\u63a5：RIGHT [OUTER]<\/span>
\n# \u5168\u5916\u8fde\u63a5：full [OUTER] mysql\u4e0d\u652f\u6301\u5168\u5916！<\/span>
\n# \u4ea4\u53c9\u8fde\u63a5：CROSS<\/span><\/p>\n

# \u5185\u8fde\u63a5：INNER<\/span>
\n\/*
\n# \u8bed\u6cd5\u683c\u5f0f：
\nselect \u67e5\u8be2\u5217\u8868
\nfrom \u88681 \u522b\u540d
\nINNER JOIN \u88682 \u522b\u540d
\nON \u8fde\u63a5\u6761\u4ef6;<\/p>\n

\u5185\u8fde\u63a5\u5206\u4e3a：\u7b49\u503c\u3001\u975e\u7b49\u503c\u3001\u81ea\u8fde\u63a5
\n\u7279\u70b9：
\n（1）\u6dfb\u52a0\u6392\u5e8f\u3001\u5206\u7ec4\u3001\u7b5b\u9009
\n（2）inner\u5173\u952e\u5b57\u53ef\u4ee5\u7701\u7565
\n（3）\u7b5b\u9009\u6761\u4ef6\u653e\u5728where\u540e\u9762，\u8fde\u63a5\u6761\u4ef6\u8981\u653e\u5728on\u540e\u9762，\u63d0\u9ad8\u5206\u79bb\u6027，\u4fbf\u4e8e\u9605\u8bfb
\n*\/<\/span>
\n# （1）\u7b49\u503c\u8fde\u63a5<\/span>
\n# eg:\u67e5\u8be2\u5458\u5de5\u540d\u3001\u90e8\u95e8\u540d<\/span>
\nselect<\/span>
\n e.<\/span>first_name,<\/span>
\n d.<\/span>department_name
\nfrom<\/span> employees AS<\/span> e
\nINNER<\/span> JOIN<\/span> departments AS<\/span> d
\nON<\/span> e.<\/span>department_id =<\/span> d.<\/span>department_id;<\/span><\/p>\n

# eg:\u67e5\u8be2\u540d\u5b57\u4e2d\u5305\u542ba\u7684\u5458\u5de5\u540d\u548c\u5de5\u79cd\u540d<\/span>
\nselect<\/span>
\n first_name,<\/span>
\n job_title
\nfrom<\/span> employees e
\nINNER<\/span> JOIN<\/span> jobs j
\nON<\/span> e.<\/span>job_id =<\/span> j.<\/span>job_id
\nWHERE<\/span>
\n e.<\/span>first_name like<\/span> '%a%'<\/span>;<\/span><\/p>\n

# eg:\u67e5\u8be2\u90e8\u95e8\u4e2a\u6570\u5927\u4e8e3\u7684\u57ce\u5e02\u540d\u548c\u90e8\u95e8\u4e2a\u6570（\u6dfb\u52a0\u5206\u7ec4 + \u7b5b\u9009）<\/span>
\n# \u5206\u6790（1）：\u67e5\u8be2\u6bcf\u4e2a\u90e8\u95e8\u7684\u4e2a\u6570<\/span>
\nselect<\/span>
\n count<\/span>(<\/span>*<\/span>)<\/span> AS<\/span> num,<\/span>
\n city
\nFROM<\/span> departments d
\nINNER<\/span> JOIN<\/span> locations l
\nON<\/span> d.<\/span>location_id =<\/span> l.<\/span>location_id
\nGROUP<\/span> BY<\/span>
\n city<\/p>\n

# \u5206\u6790（2）：\u6839\u636e（1）\u7684\u7ed3\u679c\u7b5b\u9009\u90e8\u95e8\u4e2a\u6570\u5927\u4e8e3<\/span>
\nselect<\/span>
\n count<\/span>(<\/span>*<\/span>)<\/span> AS<\/span> num,<\/span>
\n city
\nFROM<\/span> departments d
\nINNER<\/span> JOIN<\/span> locations l
\nON<\/span> d.<\/span>location_id =<\/span> l.<\/span>location_id
\nGROUP<\/span> BY<\/span>
\n city
\nHAVING<\/span>
\n num ><\/span> 3<\/span>;<\/span>
\n# eg:\u67e5\u8be2\u54ea\u4e2a\u90e8\u95e8\u7684\u5458\u5de5\u4e2a\u6570\u5927\u4e8e3\u7684\u90e8\u95e8\u540d\u548c\u5458\u5de5\u4e2a\u6570，\u5e76\u6309\u4e2a\u6570\u964d\u5e8f（\u6dfb\u52a0\u6392\u5e8f\u6761\u4ef6）<\/span>
\n# \u5206\u6790（1）\u67e5\u8be2\u6bcf\u4e2a\u90e8\u95e8\u7684\u5458\u5de5\u4e2a\u6570<\/span>
\nSELECT<\/span>
\n COUNT<\/span>(<\/span>*<\/span>)<\/span> as<\/span> num,<\/span>
\n department_name
\nFROM<\/span> employees e
\nINNER<\/span> JOIN<\/span> departments d
\nON<\/span> e.<\/span>department_id =<\/span> d.<\/span>department_id
\nGROUP<\/span> BY<\/span>
\n department_name<\/p>\n

# \u5206\u6790（2）\u6839\u636e（1）\u7684\u7ed3\u679c\u7b5b\u9009\u5458\u5de5\u4e2a\u6570\u5927\u4e8e3\u7684\u5e76\u6392\u5e8f<\/span>
\nSELECT<\/span>
\n COUNT<\/span>(<\/span> *<\/span> )<\/span> AS<\/span> num,<\/span>
\n department_name
\nFROM<\/span>
\n employees e
\n INNER<\/span> JOIN<\/span> departments d ON<\/span> e.<\/span>department_id =<\/span> d.<\/span>department_id
\nGROUP<\/span> BY<\/span>
\n department_name
\nHAVING<\/span>
\n num ><\/span> 3<\/span>
\nORDER<\/span> BY<\/span>
\n COUNT<\/span>(<\/span> *<\/span> )<\/span> DESC<\/span>;<\/span>
\n# （2）\u975e\u7b49\u503c\u8fde\u63a5<\/span>
\n# eg:\u67e5\u8be2\u5458\u5de5\u7684\u5de5\u8d44\u7ea7\u522b<\/span>
\n\/*
\n\u5206\u6790：
\n \u67e5\u8be2\u7684\u8868：employees job_grades
\n \u67e5\u8be2\u601d\u8def：\u67e5\u8be2employees\u8868\u4e2d\u7684salary \u5b57\u6bb5\u5728 job_grades \u7684\u6700\u4f4e\u5de5\u8d44\u548c\u6700\u9ad8\u5de5\u8d44\u533a\u95f4\u5185 \u786e\u5b9a\u7b49\u7ea7
\n*\/<\/span>
\nSELECT<\/span>
\n salary,<\/span>
\n grade_level
\nfrom<\/span>
\n employees e
\n INNER<\/span> JOIN<\/span> job_grades g
\n ON<\/span> e.<\/span>salary BETWEEN<\/span> g.<\/span>lowest_sal AND<\/span> g.<\/span>highest_sal;<\/span><\/p>\n

# eg:\u67e5\u8be2\u5de5\u8d44\u7ea7\u522b\u7684\u4e2a\u6570\u5927\u4e8e20\u7684\u4e2a\u6570，\u5e76\u4e14\u6309\u5de5\u8d44\u7ea7\u522b\u964d\u5e8f<\/span>
\nSELECT<\/span>
\n COUNT<\/span>(<\/span>*<\/span>)<\/span>,<\/span>
\n grade_level
\nFROM<\/span>
\n employees e
\n INNER<\/span> JOIN<\/span> job_grades g
\n ON<\/span> e.<\/span>salary BETWEEN<\/span> g.<\/span>lowest_sal AND<\/span> g.<\/span>highest_sal
\nGROUP<\/span> BY<\/span>
\n grade_level
\nHAVING<\/span>
\n COUNT<\/span>(<\/span>*<\/span>)<\/span> ><\/span> 20<\/span>
\nORDER<\/span> BY<\/span>
\n grade_level DESC<\/span>;<\/span>
\n# （3）\u81ea\u8fde\u63a5<\/span>
\n# eg:\u67e5\u8be2\u5458\u5de5\u7684\u540d\u5b57\u3001\u4e0a\u7ea7\u7684\u540d\u5b57<\/span>
\nSELECT<\/span>
\n e.<\/span>first_name AS<\/span> \u5458\u5de5,<\/span>
\n m.<\/span>first_name AS<\/span> \u9886\u5bfc
\nFROM<\/span>
\n employees e
\n INNER<\/span> JOIN<\/span> employees m
\n ON<\/span> e.<\/span>manager_id =<\/span> m.<\/span>employee_id<\/p>\n

# eg:\u67e5\u8be2\u540d\u4e2d\u5305\u542b\u5b57\u7b26a\u7684\u5458\u5de5\u540d\u5b57\u3001\u4e0a\u7ea7\u540d\u5b57<\/span>
\nSELECT<\/span>
\n e.<\/span>first_name AS<\/span> \u5458\u5de5,<\/span>
\n m.<\/span>first_name AS<\/span> \u9886\u5bfc
\nFROM<\/span>
\n employees e
\n INNER<\/span> JOIN<\/span> employees m
\n ON<\/span> e.<\/span>manager_id =<\/span> m.<\/span>employee_id
\nWHERE<\/span>
\n e.<\/span>first_name LIKE<\/span> '%a%'<\/span>;<\/span>
\n \u5916\u8fde\u63a5：
\n # \u5de6\u5916\u8fde\u63a5 LEFT [OUTER]<\/span>
\n # \u53f3\u5916\u8fde\u63a5 RIGHT [OUTER]<\/span>
\n\/*
\n\u5e94\u7528\u573a\u666f：\u7528\u4e8e\u67e5\u8be2\u4e00\u4e2a\u8868\u4e2d\u6709，\u53e6\u4e00\u4e2a\u8868\u4e2d\u6ca1\u6709\u7684\u8bb0\u5f55\u3002
\n\u7279\u70b9\u603b\u7ed3：
\n (1)\u5916\u8fde\u63a5\u7684\u67e5\u8be2\u7ed3\u679c\u4e3a\u4e3b\u8868\u4e2d\u7684\u6240\u6709\u8bb0\u5f55，\u5982\u679c\u4ece\u8868\u4e2d\u6709\u548c\u5b83\u5339\u914d\u7684，\u5219\u663e\u793a\u5339\u914d\u7684\u503c，\u5982\u679c\u4ece\u8868\u4e2d\u6ca1\u6709\u548c\u5b83\u5339\u914d\u7684\u5219\u663e\u793anull；
\n \u5916\u8fde\u63a5\u67e5\u8be2\u7ed3\u679c = \u5185\u8fde\u63a5\u7ed3\u679c + \u4e3b\u8868\u4e2d\u6709\u4ece\u8868\u4e2d\u6ca1\u6709\u7684\u8bb0\u5f55<\/p>\n

(2)\u5de6\u5916\u8fde\u63a5，left join\u5de6\u8fb9\u662f\u4e3b\u8868，\u53f3\u8fb9\u662f\u4ece\u8868；\u53f3\u5916\u8fde\u63a5，right join\u53f3\u8fb9\u662f\u4e3b\u8868，\u5de6\u8fb9\u662f\u4ece\u8868<\/p>\n

(3)\u5de6\u5916\u548c\u53f3\u5916\u4ea4\u6362\u4e24\u4e2a\u8868\u7684\u987a\u5e8f，\u53ef\u4ee5\u5b9e\u73b0\u76f8\u540c\u7684\u7ed3\u679c<\/p>\n

(4)\u5168\u5916\u8fde\u63a5 = \u5185\u8fde\u63a5\u7ed3\u679c + \u88681\u4e2d\u6709\u4f46\u88682\u4e2d\u6ca1\u6709\u7684 + \u88682\u4e2d\u6709\u4f46\u88681\u4e2d\u6ca1\u6709\u7684<\/p>\n

A left join B
\nA right join B<\/p>\n

\u8fde\u63a5\u7c7b\u578b \u5173\u952e\u5b57 \u4fdd\u7559\u7684\u8bb0\u5f55 \u672a\u5339\u914d\u65f6\u7684\u5904\u7406
\n\u5de6\u5916\u8fde\u63a5LEFT JOIN \u6216 LEFT OUTER JOIN \u5de6\u8868\u5168\u90e8\u8bb0\u5f55 \u53f3\u8868\u5b57\u6bb5\u586b\u5145NULL
\n\u53f3\u5916\u8fde\u63a5RIGHT JOIN \u6216 RIGHT OUTER JOIN\u53f3\u8868\u5168\u90e8\u8bb0\u5f55 \u5de6\u8868\u5b57\u6bb5\u586b\u5145NULL
\n\u5168\u5916\u8fde\u63a5FULL JOIN \u6216 FULL OUTER JOIN \u4e24\u8868\u5168\u90e8\u8bb0\u5f55 \u7f3a\u5931\u65b9\u5b57\u6bb5\u586b\u5145NULL<\/p>\n

\u5bf9\u6bd4\u7ef4\u5ea6 LEFT JOIN RIGHT JOIN FULL JOIN
\n\u4fdd\u7559\u8868 \u5de6\u8868\u5168\u90e8 \u53f3\u8868\u5168\u90e8 \u4e24\u8868\u5168\u90e8
\n\u5339\u914d\u5931\u8d25\u586b\u5145\u53f3\u8868\u5b57\u6bb5\u4e3aNULL \u5de6\u8868\u5b57\u6bb5\u4e3aNULL \u5bf9\u5e94\u65b9\u5b57\u6bb5\u4e3aNULL
\n\u662f\u5426\u53ef\u4e92\u6362 \u53ef\u4ee5（\u8c03\u6362\u8868\u987a\u5e8f）\u53ef\u4ee5（\u8c03\u6362\u8868\u987a\u5e8f）\u4e0d\u53ef\u4ee5（\u9700UNION\u6a21\u62df）
\nMySQL\u539f\u751f\u652f\u6301 \u2705 \u652f\u6301 \u2705 \u652f\u6301 \u274c \u4e0d\u652f\u6301<\/p>\n

\u67e5\u8be2 \u5305\u542bA\u72ec\u6709\u5305\u542b\u4ea4\u96c6\u5305\u542bB\u72ec\u6709\u7ed3\u679c\u96c6\u8303\u56f4
\nLEFT JOIN \u2705 \u2705 \u274c A\u5168\u90e8
\nRIGHT JOIN \u274c \u2705 \u2705 B\u5168\u90e8
\nINNER JOIN \u274c \u2705 \u274c \u4ea4\u96c6
\nLEFT + WHERE B IS NULL \u2705 \u274c \u274c A\u72ec\u6709（A-B）
\nFULL + WHERE A IS NULL \u274c \u274c \u2705 B\u72ec\u6709（B-A）
\nFULL JOIN\u2705\u2705\u2705\u5e76\u96c6<\/p>\n

*\/<\/span>
\n# \u5f15\u5165：\u67e5\u8be2\u7537\u670b\u53cb\u4e0d\u5728\u7537\u795e\u8868\u4e2d\u7684\u5973\u795e\u540d<\/span>
\n# \u67e5\u8be2\u6ca1\u6709\u7537\u670b\u53cb\u7684\u5973\u795e<\/span><\/p>\n

# \u5de6\u5916\u8fde\u63a5：<\/span><\/p>\n

SELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n beauty b
\n LEFT<\/span> JOIN<\/span> boys bo
\n ON<\/span> b.<\/span>boyfriend_id =<\/span> bo.<\/span>id
\nWHERE<\/span>
\n bo.<\/span>id is<\/span> NULL<\/span>;<\/span><\/p>\n

# \u53f3\u5916\u8fde\u63a5：<\/span>
\nSELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n boys bo
\n RIGHT<\/span> JOIN<\/span> beauty b
\n ON<\/span> bo.<\/span>id =<\/span> b.<\/span>boyfriend_id
\nWHERE<\/span>
\n bo.<\/span>id is<\/span> NOT<\/span> NULL<\/span>;<\/span>
\n# eg：\u67e5\u8be2\u54ea\u4e2a\u90e8\u95e8\u6ca1\u6709\u5458\u5de5\u3002<\/span>
\n# \u5de6\u5916\u8fde\u63a5 ：\u90e8\u95e8\u8868 \u4e3b\u8868 \u5458\u5de5\u8868 \u4ece\u8868<\/span><\/p>\n

SELECT<\/span>
\n d.<\/span>*<\/span>,<\/span>
\n e.<\/span>employee_id
\nFROM<\/span>
\n departments d
\n LEFT<\/span> JOIN<\/span> employees e
\n ON<\/span> d.<\/span>department_id =<\/span> e.<\/span>department_id
\nWHERE<\/span>
\n e.<\/span>employee_id IS<\/span> NULL<\/span>;<\/span><\/p>\n

#\u53f3\u5916\u8fde\u63a5<\/span>
\nSELECT<\/span>
\n d.<\/span>*<\/span>,<\/span>
\n e.<\/span>employee_id
\nFROM<\/span>
\n employees e
\n RIGHT<\/span> JOIN<\/span> departments d
\n ON<\/span> e.<\/span>department_id =<\/span> d.<\/span>department_id
\nWHERE<\/span>
\n e.<\/span>employee_id IS<\/span> NULL<\/span>;<\/span><\/p>\n

# \u5168\u5916\u8fde\u63a5（mysql\u4e0d\u652f\u6301\u5168\u5916\u8fde\u63a5）<\/span>
\n— SELECT<\/span>
\n— *<\/span>
\n— FROM<\/span>
\n— beauty b <\/span>
\n— FULL JOIN boys bo <\/span>
\n— ON b.boyfriend_id = bo.id;<\/span><\/p>\n

# \u4ea4\u53c9\u8fde\u63a5（\u7b1b\u5361\u5c14\u79ef）<\/span>
\nSELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n beauty b
\n CROSS<\/span> JOIN<\/span> boys bo ;<\/span><\/p>\n

(7)，\u5b50\u67e5\u8be2 [\u5b50\u67e5\u8be2：\u51fa\u73b0\u5728\u5176\u4ed6\u8bed\u53e5\u4e2d\u7684select\u8bed\u53e5，\u79f0\u4e4b\u4e3a\u5b50\u67e5\u8be2（\u5185\u67e5\u8be2） \u5206\u7c7b： \u6309\u5b50\u67e5\u8be2\u51fa\u73b0\u7684\u4f4d\u7f6e\u53ef\u5206： （1）select\u540e\u9762：\u4ec5\u652f\u6301\u6807\u91cf\u5b50\u67e5\u8be2\u3002 （2）where\u6216\u8005having\u540e\u9762：\u652f\u6301\u6807\u91cf\u5b50\u67e5\u8be2（\u5355\u884c）\u3001\u5217\u5b50\u67e5\u8be2（\u591a\u884c）\u3001\u884c\u5b50\u67e5\u8be2 （3）exists\u540e\u9762（\u76f8\u5173\u5b50\u67e5\u8be2）：\u652f\u6301\u8868\u5b50\u67e5\u8be2 （4）from\u540e\u9762\u8ddf\u5b50\u67e5\u8be2 \u6309\u7ed3\u679c\u96c6\u7684\u884c\u6570\u53ef\u5206： （1）\u6807\u91cf\u5b50\u67e5\u8be2（\u7ed3\u679c\u53ea\u6709\u4e00\u884c\u4e00\u5217） （2）\u5217\u5b50\u67e5\u8be2（\u7ed3\u679c\u53ea\u6709\u4e00\u5217\u591a\u884c） （3）\u884c\u5b50\u67e5\u8be2（\u7ed3\u679c\u6709\u4e00\u884c\u591a\u5217） （4）\u8868\u5b50\u67e5\u8be2（\u7ed3\u679c\u591a\u884c\u591a\u5217）]<\/p>\n

\/*
\n\u5b50\u67e5\u8be2：\u51fa\u73b0\u5728\u5176\u4ed6\u8bed\u53e5\u4e2d\u7684select\u8bed\u53e5，\u79f0\u4e4b\u4e3a\u5b50\u67e5\u8be2（\u5185\u67e5\u8be2）
\n\u5206\u7c7b：
\n\u6309\u5b50\u67e5\u8be2\u51fa\u73b0\u7684\u4f4d\u7f6e\u53ef\u5206：
\n （1）select\u540e\u9762：\u4ec5\u652f\u6301\u6807\u91cf\u5b50\u67e5\u8be2\u3002
\n （2）where\u6216\u8005having\u540e\u9762：\u652f\u6301\u6807\u91cf\u5b50\u67e5\u8be2（\u5355\u884c）\u3001\u5217\u5b50\u67e5\u8be2（\u591a\u884c）\u3001\u884c\u5b50\u67e5\u8be2
\n （3）exists\u540e\u9762（\u76f8\u5173\u5b50\u67e5\u8be2）：\u652f\u6301\u8868\u5b50\u67e5\u8be2
\n （4）from\u540e\u9762\u8ddf\u5b50\u67e5\u8be2
\n\u6309\u7ed3\u679c\u96c6\u7684\u884c\u6570\u53ef\u5206：
\n （1）\u6807\u91cf\u5b50\u67e5\u8be2（\u7ed3\u679c\u53ea\u6709\u4e00\u884c\u4e00\u5217）
\n （2）\u5217\u5b50\u67e5\u8be2（\u7ed3\u679c\u53ea\u6709\u4e00\u5217\u591a\u884c）
\n （3）\u884c\u5b50\u67e5\u8be2（\u7ed3\u679c\u6709\u4e00\u884c\u591a\u5217）
\n （4）\u8868\u5b50\u67e5\u8be2（\u7ed3\u679c\u591a\u884c\u591a\u5217）
\n*\/<\/span>
\n— 1\u3001where\u6216\u8005having\u540e\u9762\u8ddf\u5b50\u67e5\u8be2<\/span>
\n\/*
\n\u7279\u70b9：
\n1\u3001\u5b50\u67e5\u8be2\u653e\u5728\u5c0f\u62ec\u53f7\u5185；
\n2\u3001\u5b50\u67e5\u8be2\u4e00\u822c\u653e\u5728\u6761\u4ef6\u7684\u53f3\u4fa7；
\n3\u3001\u6807\u91cf\u5b50\u67e5\u8be2，\u4e00\u822c\u642d\u914d\u7740\u5355\u884c\u64cd\u4f5c\u7b26\u4f7f\u7528： > < >= <= !=\/<> <=>
\n4\u3001\u5217\u5b50\u67e5\u8be2，\u4e00\u822c\u642d\u914d\u7740\u591a\u884c\u64cd\u4f5c\u7b26\u4f7f\u7528： in any\/some all
\n5\u3001\u5b50\u67e5\u8be2\u7684\u6267\u884c\u7531\u4e8e\u4e3b\u67e5\u8be2\u6267\u884c，\u4e3b\u67e5\u8be2\u7684\u6761\u4ef6\u7528\u5230\u4e86\u5b50\u67e5\u8be2\u7684\u7ed3\u679c（\u865a\u8868）
\n*\/<\/span>
\n–（1）\u6807\u91cf\u5b50\u67e5\u8be2<\/span>
\n# eg:\u8c01\u7684\u5de5\u8d44\u6bd4Lex\u7684\u9ad8\u3002<\/span>
\nselect<\/span> *<\/span>
\nfrom<\/span> employees
\nwhere<\/span> salary ><\/span> (<\/span>select<\/span> salary from<\/span> employees where<\/span> first_name =<\/span> 'Lex'<\/span>)<\/span>
\n# eg :\u8fd4\u56dejob_id\u4e0e141\u53f7\u5458\u5de5\u76f8\u540c，salary\u6bd4143\u53f7\u5458\u5de5\u591a\u7684\u5458\u5de5\u540d\u3001job_id\u548c\u5de5\u8d44<\/span>
\nselect<\/span> first_name ,<\/span> job_id ,<\/span> salary
\nfrom<\/span> employees
\nwhere<\/span>
\njob_id =<\/span> (<\/span>select<\/span> job_id from<\/span> employees where<\/span> job_id =<\/span> 141<\/span> )<\/span>
\nsalary ><\/span> (<\/span>select<\/span> salary from<\/span> employees where<\/span> employee_id =<\/span> 143<\/span> )<\/span>;<\/span>
\n# eg:\u8fd4\u56de\u516c\u53f8\u5de5\u8d44\u6700\u5c11\u7684\u5458\u5de5\u7684 last_name\u3001job_id\u3001salary<\/span>
\nselect<\/span> last_name,<\/span>job_id,<\/span>salary
\nfrom<\/span> employees
\nwhere<\/span> salary =<\/span> (<\/span>select<\/span> a from<\/span> employees where<\/span> min<\/span>(<\/span>salary as<\/span> a)<\/span> )<\/span>;<\/span>
\n# eg:\u67e5\u8be2\u6700\u4f4e\u5de5\u8d44\u5927\u4e8e50\u53f7\u90e8\u95e8\u6700\u4f4e\u5de5\u8d44\u7684\u90e8\u95e8id\u548c\u5176\u6700\u4f4e\u5de5\u8d44<\/span>
\n# （1）\u67e5\u8be250\u53f7\u90e8\u95e8\u6700\u4f4e\u5de5\u8d44<\/span>
\nSELECT<\/span>
\n min<\/span>(<\/span>salary)<\/span>
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n department_id =<\/span> 50<\/span><\/p>\n

# (2)\u67e5\u8be2\u6bcf\u4e2a\u90e8\u95e8\u7684\u6700\u4f4e\u5de5\u8d44<\/span>
\nSELECT<\/span>
\n min<\/span>(<\/span>salary)<\/span>,<\/span>
\n department_id
\nFROM<\/span>
\n employees
\nGROUP<\/span> BY<\/span>
\n department_id<\/p>\n

# （3）\u5728（2） \u7684\u57fa\u7840\u4e0a，\u6ee1\u8db3 min(salary) > (1)\u7684\u7ed3\u679c<\/span>
\nSELECT<\/span>
\n min<\/span>(<\/span> salary )<\/span>,<\/span>
\n department_id
\nFROM<\/span>
\n employees
\nGROUP<\/span> BY<\/span>
\n department_id
\nHAVING<\/span>
\n min<\/span>(<\/span> salary )<\/span> ><\/span> (<\/span> SELECT<\/span> min<\/span>(<\/span> salary )<\/span> FROM<\/span> employees WHERE<\/span> department_id =<\/span> 50<\/span> )<\/span>;<\/span>
\n# \u6ce8\u610f：\u975e\u6cd5\u4f7f\u7528\u6807\u91cf\u5b50\u67e5\u8be2<\/span>
\n# min( salary ) > \u786e\u5b9a\u7684\u503c<\/span>
\n# min( salary ) > \u5f88\u591a\u503c \u9519\u8bef，\u975e\u6cd5\u4f7f\u7528！！！<\/span><\/p>\n

–（2）\u5217\u5b50\u67e5\u8be2（\u591a\u884c）<\/span>
\n\/*
\nin \/ not in:\u7b49\u4e8e\u5217\u8868\u4e2d\u7684\u4efb\u610f\u4e00\u4e2a
\nany \/ some ：\u548c\u5b50\u67e5\u8be2\u8fd4\u56de\u7684\u67d0\u4e00\u4e2a\u503c\u8fdb\u884c\u6bd4\u8f83
\nall：\u548c\u5b50\u67e5\u8be2\u8fd4\u56de\u7684\u6240\u6709\u503c\u6bd4\u8f83
\n*\/<\/span>
\n# eg:\u8fd4\u56de location_id \u662f 1400 \u6216\u8005 1700 \u7684\u90e8\u95e8\u4e2d\u7684\u6240\u6709\u5458\u5de5\u540d<\/span>
\n# （1）\u67e5\u8be2 location_id\u662f 1400 \u6216\u8005 1700\u7684\u90e8\u95e8\u7f16\u53f7<\/span>
\nSELECT<\/span> DISTINCT<\/span>
\n department_id
\nFROM<\/span>
\n departments
\nWHERE<\/span>
\n location_id in<\/span> (<\/span>1400<\/span>,<\/span>1700<\/span>)<\/span><\/p>\n

# (2) \u67e5\u8be2\u5458\u5de5\u540d，\u8981\u6c42\u90e8\u95e8\u53f7\u662f：（1）\u7ed3\u679c\u4e2d\u7684\u67d0\u4e00\u4e2a<\/span>
\nSELECT<\/span>
\n first_name
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n department_id IN<\/span> (<\/span> SELECT<\/span> DISTINCT<\/span> department_id FROM<\/span> departments WHERE<\/span> location_id IN<\/span> (<\/span> 1400<\/span>,<\/span> 1700<\/span> )<\/span> )<\/span>;<\/span>
\n# eg: \u8fd4\u56de\u5176\u4ed6\u5de5\u79cd\u4e2d\u6bd4job_id\u4e3a：IT_PROG \u5de5\u79cd\u4efb\u4e00\u5de5\u8d44\u4f4e\u7684\u5458\u5de5\u7684\u5de5\u53f7\u3001\u540d\u3001job_id\u4ee5\u53ca salary<\/span>
\n# （1） \u67e5\u8be2 job_id \u4e3a IT_PROG \u5de5\u8d44\u7684\u4efb\u4e00\u5de5\u8d44<\/span>
\nSELECT<\/span> DISTINCT<\/span>
\n salary
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n job_id =<\/span> 'IT_PROG'<\/span><\/p>\n

# (2) \u67e5\u8be2\u5458\u5de5\u7684\u5de5\u53f7\u3001\u540d\u3001job_id\u4ee5\u53casalary，\u8981\u6c42 salary < (1) \u4efb\u610f\u4e00\u4e2a<\/span><\/p>\n

SELECT<\/span>
\n employee_id,<\/span>
\n first_name,<\/span>
\n job_id,<\/span>
\n salary
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n salary <<\/span> ANY<\/span> (<\/span> SELECT<\/span> DISTINCT<\/span> salary FROM<\/span> employees WHERE<\/span> job_id =<\/span> 'IT_PROG'<\/span> )<\/span>;<\/span><\/p>\n

— \u5c0f\u4e8e\u6700\u5927\u7684<\/span><\/p>\n

SELECT<\/span>
\n employee_id,<\/span>
\n first_name,<\/span>
\n job_id,<\/span>
\n salary
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n salary <<\/span> (<\/span> SELECT<\/span> max<\/span>(<\/span>salary)<\/span> FROM<\/span> employees WHERE<\/span> job_id =<\/span> 'IT_PROG'<\/span> )<\/span>;<\/span>
\n# eg:\u8fd4\u56de\u5176\u4ed6\u5de5\u79cd\u4e2d\u6bd4 job_id \u4e3a：IT_PROG\u5de5\u79cd\u6240\u6709\u5de5\u8d44\u4f4e\u7684\u5458\u5de5\u7684\u5de5\u53f7\u3001\u540d\u3001job_id\u4ee5\u53casalary<\/span><\/p>\n

# eg:\u8fd4\u56de\u5176\u4ed6\u5de5\u79cd\u4e2d\u6bd4 job_id \u4e3a：IT_PROG\u5de5\u79cd\u6240\u6709\u5de5\u8d44\u4f4e\u7684\u5458\u5de5\u7684\u5de5\u53f7\u3001\u540d\u3001job_id\u4ee5\u53casalary<\/span><\/p>\n

# （1）\u67e5\u8be2job_id \u4e3a：IT_PROG \u7684\u4efb\u4e00\u5de5\u8d44<\/span>
\nSELECT<\/span> DISTINCT<\/span>
\n salary
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n job_id =<\/span> 'IT_PROG'<\/span><\/p>\n

# (2) \u67e5\u8be2\u5458\u5de5\u7684\u5de5\u53f7\u3001\u540d\u3001job_id\u4ee5\u53casalary，\u8981\u6c42 salary < (1) \u7684\u6240\u6709<\/span><\/p>\n

SELECT<\/span>
\n employee_id,<\/span>
\n first_name,<\/span>
\n job_id,<\/span>
\n salary
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n salary <<\/span> ALL<\/span> (<\/span> SELECT<\/span> DISTINCT<\/span> salary FROM<\/span> employees WHERE<\/span> job_id =<\/span> 'IT_PROG'<\/span> )<\/span>;<\/span>
\n — \u5c0f\u4e8e\u6700\u5c0f\u7684<\/span><\/p>\n

SELECT<\/span>
\n employee_id,<\/span>
\n first_name,<\/span>
\n job_id,<\/span>
\n salary
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n salary <<\/span> (<\/span> SELECT<\/span> min<\/span>(<\/span>salary)<\/span> FROM<\/span> employees WHERE<\/span> job_id =<\/span> 'IT_PROG'<\/span> )<\/span>;<\/span>
\n–(3)\u884c\u5b50\u67e5\u8be2<\/span>
\n# eg:\u67e5\u8be2\u5458\u5de5\u7f16\u53f7\u6700\u5c0f\u5e76\u4e14\u5de5\u8d44\u6700\u9ad8\u7684\u5458\u5de5\u4fe1\u606f\u3002<\/span>
\nSELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n employee_id =<\/span> (<\/span> SELECT<\/span> MIN<\/span>(<\/span> employee_id )<\/span> FROM<\/span> employees )<\/span>
\n AND<\/span> salary =<\/span> (<\/span> SELECT<\/span> MAX<\/span>(<\/span> salary )<\/span> FROM<\/span> employees )<\/span>;<\/span>
\n — 2\u3001select \u540e\u9762\u8ddf\u5b50\u67e5\u8be2<\/span>
\n \/*
\n\u4ec5\u652f\u6301\u6807\u91cf\u5b50\u67e5\u8be2
\n*\/<\/span>
\n# eg:\u67e5\u8be2\u6bcf\u4e2a\u90e8\u95e8\u7684\u5458\u5de5\u4e2a\u6570<\/span>
\nSELECT<\/span>
\n d.<\/span>*<\/span>,<\/span>
\n (<\/span>select<\/span> count<\/span>(<\/span>*<\/span>)<\/span> from<\/span> employees e where<\/span> e.<\/span>department_id =<\/span> d.<\/span>department_id)<\/span> \u4e2a\u6570
\nFROM<\/span> departments d
\n# eg:\u67e5\u8be2\u5458\u5de5\u5de5\u53f7\u7b49\u4e8e102\u7684\u90e8\u95e8\u540d<\/span>
\nSELECT<\/span>
\n (<\/span>
\n select<\/span>
\n department_name
\n FROM<\/span>
\n departments d
\n INNER<\/span> JOIN<\/span> employees e
\n ON<\/span> d.<\/span>department_id =<\/span> e.<\/span>department_id
\n WHERE<\/span>
\n e.<\/span>employee_id =<\/span> 102<\/span>
\n )<\/span> \u90e8\u95e8\u540d;<\/span>
\n— 3\u3001from\u540e\u9762\u8ddf\u5b50\u67e5\u8be2<\/span>
\n\/*
\n\u5c06\u5b50\u67e5\u8be2\u7684\u7ed3\u679c\u5145\u5f53\u4e00\u5f20\u8868，\u8981\u6c42\u5fc5\u987b\u53d6\u522b\u540d
\n*\/<\/span>
\n# eg:\u67e5\u8be2\u6bcf\u4e2a\u90e8\u95e8\u7684\u5e73\u5747\u5de5\u8d44\u7b49\u7ea7<\/span>
\n# （1） \u67e5\u8be2\u6bcf\u4e2a\u90e8\u95e8\u7684\u5e73\u5747\u5de5\u8d44<\/span>
\nSELECT<\/span>
\n ROUND<\/span>(<\/span>avg<\/span>(<\/span>salary)<\/span>)<\/span>,<\/span>
\n department_id
\nFROM<\/span>
\n employees
\nGROUP<\/span> BY<\/span>
\n department_id<\/p>\n

# (2) \u8fde\u63a5（1）\u7684\u7ed3\u679c\u548c job_grades \u8868，\u7b5b\u9009\u6761\u4ef6\u5e73\u5747\u5de5\u8d44 between lowest_sal and highest_sal<\/span>
\nSELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n (<\/span> SELECT<\/span> ROUND<\/span>(<\/span> avg<\/span>(<\/span> salary )<\/span> )<\/span> ag,<\/span> department_id FROM<\/span> employees GROUP<\/span> BY<\/span> department_id )<\/span> ag_dep
\n INNER<\/span> JOIN<\/span> job_grades g ON<\/span> ag_dep.<\/span>ag BETWEEN<\/span> lowest_sal AND<\/span> highest_sal;<\/span>
\n— 4\u3001exists\u540e\u9762<\/span>
\n\/*
\n\u8bed\u6cd5：
\nexists （\u5b8c\u6574sql\u8bed\u53e5）
\n\u7ed3\u679c：1（\u771f） \u6216\u8005 0 （\u5047）<\/p>\n

*\/<\/span>
\nSELECT<\/span> EXISTS<\/span>(<\/span>SELECT<\/span> employee_id FROM<\/span> employees WHERE<\/span> salary =<\/span> 80000<\/span>)<\/span>;<\/span>–\u8fd4\u56de0<\/span>
\n# eg:\u67e5\u8be2\u6709\u5458\u5de5\u7684\u90e8\u95e8\u540d<\/span>
\nSELECT<\/span>
\n department_name
\nFROM<\/span>
\n departments d
\nWHERE<\/span>
\n EXISTS<\/span> (<\/span>select<\/span> *<\/span> from<\/span> employees e WHERE<\/span> d.<\/span>department_id =<\/span> e.<\/span>department_id)<\/span>;<\/span>—\u8fd4\u56de\u6240\u6709employees \u4e2d\u5b58\u5728\u7684department_id <\/span><\/p>\n

SELECT<\/span>
\n department_name
\nFROM<\/span>
\n departments d
\nWHERE<\/span>
\n d.<\/span>department_id IN<\/span> (<\/span>SELECT<\/span> department_id from<\/span> employees)<\/span><\/p>\n

（8）\u5206\u9875\u67e5\u8be2 [– \u603b\u7ed3\u5206\u9875\u67e5\u8be2<\/p>\n

select \u67e5\u8be2\u5217\u8868 (7) from \u8868\u540d (1) [ join type join \u88682 (2) on \u8fde\u63a5\u6761\u4ef6 (3) where \u7b5b\u9009\u6761\u4ef6 (4) group by \u5206\u7ec4\u5b57\u6bb5 (5) having \u5206\u7ec4\u540e\u7b5b\u9009 (6) order by \u6392\u5e8f\u5b57\u6bb5 (8) ] limit [offset] size; (9)<\/p>\n

offset:\u8981\u663e\u793a\u6761\u76ee\u6570\u7684\u8d77\u59cb\u7d22\u5f15（\u9ed8\u8ba4\u8d77\u59cb\u7d22\u5f15\u4ece0\u5f00\u59cb） size：\u8981\u663e\u793a\u7684\u6761\u76ee\u4e2a\u6570<\/p>\n

\u6ce8\u610f： （1）limit\u8bed\u53e5\u653e\u5728\u67e5\u8be2\u8bed\u53e5\u7684\u6700\u540e （2）\u516c\u5f0f： \u8981\u663e\u793a\u7684\u9875\u6570（page），\u6bcf\u9875\u7684\u6761\u76ee\u6570（size） limit （page – 1） * size,size page 1 0 2 25 3 50 ]<\/p>\n

\/*
\n\u5e94\u7528\u573a\u666f：\u5f53\u8981\u663e\u793a\u7684\u6570\u636e，\u4e00\u9875\u663e\u793a\u4e0d\u5168，\u9700\u8981\u5206\u9875\u63d0\u4ea4sql\u8bf7\u6c42
\n\u8bed\u6cd5\u683c\u5f0f：
\n— \u603b\u7ed3\u5206\u9875\u67e5\u8be2
\nselect \u67e5\u8be2\u5217\u8868 (7)
\nfrom \u8868\u540d (1)
\n[
\n join type join \u88682 (2)
\n on \u8fde\u63a5\u6761\u4ef6 (3)
\n where \u7b5b\u9009\u6761\u4ef6 (4)
\n group by \u5206\u7ec4\u5b57\u6bb5 (5)
\n having \u5206\u7ec4\u540e\u7b5b\u9009 (6)
\n order by \u6392\u5e8f\u5b57\u6bb5 (8)
\n]
\nlimit [offset] size; (9)
\noffset:\u8981\u663e\u793a\u6761\u76ee\u6570\u7684\u8d77\u59cb\u7d22\u5f15（\u9ed8\u8ba4\u8d77\u59cb\u7d22\u5f15\u4ece0\u5f00\u59cb）
\nsize：\u8981\u663e\u793a\u7684\u6761\u76ee\u4e2a\u6570<\/p>\n

\u6ce8\u610f：
\n （1）limit\u8bed\u53e5\u653e\u5728\u67e5\u8be2\u8bed\u53e5\u7684\u6700\u540e
\n （2）\u516c\u5f0f：
\n \u8981\u663e\u793a\u7684\u9875\u6570（page），\u6bcf\u9875\u7684\u6761\u76ee\u6570（size）
\n limit （page – 1） * size,size
\n page
\n 1 0
\n 2 25
\n 3 50
\n*\/<\/span>
\n# eg:\u67e5\u8be2\u524d\u4e94\u6761\u5458\u5de5\u4fe1\u606f<\/span>
\nSELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n employees
\nLIMIT<\/span> 5<\/span>;<\/span><\/p>\n

SELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n employees
\nLIMIT<\/span> 2<\/span>,<\/span> 5<\/span>;<\/span>
\n# eg:\u67e5\u8be2\u5458\u5de5\u8868\u7b2c11\u6761\u6570\u636e\u5230\u7b2c25\u6761\u6570\u636e<\/span>
\nSELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n employees<\/p>\n

LIMIT<\/span> 10<\/span>,<\/span>15<\/span>;<\/span>
\n# eg:\u6709\u5956\u91d1\u7387\u7684\u5458\u5de5\u4fe1\u606f，\u5e76\u4e14\u5de5\u8d44\u8f83\u9ad8\u7684\u524d10\u540d<\/span>
\nSELECT<\/span>
\n *<\/span>
\nFROM<\/span>
\n employees
\nWHERE<\/span>
\n commission_pct is<\/span> not<\/span> null<\/span>
\nORDER<\/span> BY<\/span>
\n salary DESC<\/span>
\nlimit<\/span> 10<\/span>;<\/span><\/p>\n

(9)union\u8054\u5408\u67e5\u8be2 [\u8bed\u6cd5\u683c\u5f0f：<\/p>\n

\u67e5\u8be2\u8bed\u53e51 union \u67e5\u8be2\u8bed\u53e52;<\/p>\n

\u5e94\u7528\u573a\u666f：\u8981\u67e5\u8be2\u7684\u7ed3\u679c\u6765\u81ea\u591a\u4e2a\u8868，\u4e14\u591a\u4e2a\u8868\u6ca1\u6709\u76f4\u63a5\u7684\u8fde\u63a5\u5173\u7cfb，\u4f46\u67e5\u8be2\u7684\u4fe1\u606f\u4e00\u81f4\u65f6 \u7279\u70b9： 1\u3001\u8981\u6c42\u591a\u6761\u67e5\u8be2\u8bed\u53e5\u7684\u67e5\u8be2\u5217\u6570\u662f\u4e00\u81f4\u7684\u3002 2\u3001\u8981\u6c42\u591a\u6761\u67e5\u8be2\u8bed\u53e5\u7684\u67e5\u8be2\u7684\u6bcf\u4e00\u5217\u7c7b\u578b\u548c\u987a\u5e8f\u6700\u597d\u4e00\u81f4\u3002 3\u3001union\u5173\u952e\u5b57\u9ed8\u8ba4\u53bb\u91cd，\u5982\u679c\u4f7f\u7528union all \u53ef\u4ee5\u5305\u542b\u91cd\u590d\u9879\u7684\u3002]<\/p>\n

–\u5c06\u591a\u6761\u67e5\u8be2\u8bed\u53e5\u7684\u7ed3\u679c\u5408\u5e76\u6210\u4e00\u4e2a\u7ed3\u679c<\/span>
\n\/*
\n\u8bed\u6cd5\u683c\u5f0f：<\/p>\n

\u67e5\u8be2\u8bed\u53e51
\n union
\n \u67e5\u8be2\u8bed\u53e52;<\/p>\n

\u5e94\u7528\u573a\u666f：\u8981\u67e5\u8be2\u7684\u7ed3\u679c\u6765\u81ea\u591a\u4e2a\u8868，\u4e14\u591a\u4e2a\u8868\u6ca1\u6709\u76f4\u63a5\u7684\u8fde\u63a5\u5173\u7cfb，\u4f46\u67e5\u8be2\u7684\u4fe1\u606f\u4e00\u81f4\u65f6
\n\u7279\u70b9：
\n 1\u3001\u8981\u6c42\u591a\u6761\u67e5\u8be2\u8bed\u53e5\u7684\u67e5\u8be2\u5217\u6570\u662f\u4e00\u81f4\u7684\u3002
\n 2\u3001\u8981\u6c42\u591a\u6761\u67e5\u8be2\u8bed\u53e5\u7684\u67e5\u8be2\u7684\u6bcf\u4e00\u5217\u7c7b\u578b\u548c\u987a\u5e8f\u6700\u597d\u4e00\u81f4\u3002
\n 3\u3001union\u5173\u952e\u5b57\u9ed8\u8ba4\u53bb\u91cd，\u5982\u679c\u4f7f\u7528union all \u53ef\u4ee5\u5305\u542b\u91cd\u590d\u9879\u7684\u3002
\n*\/<\/span>
\n# eg:\u67e5\u8be2\u90e8\u95e8\u7f16\u53f7\u5927\u4e8e90\u6216\u90ae\u7bb1\u5305\u542be\u7684\u5458\u5de5\u4fe1\u606f<\/span>
\nSELECT<\/span> *<\/span> FROM<\/span> employees WHERE<\/span> department_id ><\/span> 90<\/span> OR<\/span> email LIKE<\/span> '%e%'<\/span>;<\/span><\/p>\n

select<\/span> *<\/span> from<\/span> employees where<\/span> department_id ><\/span> 90<\/span>
\nunion<\/span>
\nselect<\/span> *<\/span> from<\/span> employees where<\/span> email LIKE<\/span> '%e%'<\/span>;<\/span><\/p>\n

5，DML\u64cd\u4f5c\u8bed\u8a00 1\u3001\u63d2\u5165：insert 2\u3001\u4fee\u6539：update 3\u3001\u5220\u9664：delete<\/p>\n

（1<\/span>）\u63d2\u5165\u65b9\u5f0f\u4e00：
\n\/*
\ninsert into \u8868\u540d (\u5217\u540d,……..) values (\u503c1,……);
\ninsert into \u8868\u540d values (\u503c1,……);<\/p>\n

（2） \u63d2\u5165\u65b9\u5f0f\u4e8c：
\ninsert into \u8868\u540d set \u5217\u540d = \u503c,\u5217\u540d = \u503c,…..<\/p>\n

\u63d2\u5165\u65b9\u5f0f\u5bf9\u6bd4：
\n（1）\u65b9\u5f0f\u4e00\u652f\u6301\u63d2\u5165\u591a\u884c，\u65b9\u5f0f\u4e8c\u4e0d\u652f\u6301
\n（2）\u65b9\u5f0f\u4e00\u652f\u6301\u5b50\u67e5\u8be2，\u65b9\u5f0f\u4e8c\u4e0d\u652f\u6301<\/p>\n

— \u603b\u7ed3：
\n（1）\u4fee\u6539\u5355\u8868\u8bb0\u5f55
\nupdate \u8868\u540d （1）
\nset \u5217 = \u65b0\u503c,\u5217 = \u65b0\u503c,….（3）
\nwhere \u7b5b\u9009\u6761\u4ef6（2）<\/p>\n

（2）\u4fee\u6539\u591a\u8868\u8bb0\u5f55(\u8865\u5145)
\nupdate \u88681 \u522b\u540d
\ninner | left | right join \u88682 \u522b\u540d
\non \u8fde\u63a5\u6761\u4ef6
\nset \u5217 = \u65b0\u503c,\u5217 = \u65b0\u503c,….
\nwhere \u7b5b\u9009\u6761\u4ef6<\/p>\n

(1)\u5355\u8868\u5220\u9664
\ndelete from \u8868\u540d where \u7b5b\u9009\u6761\u4ef6;<\/p>\n

（2）\u591a\u8868\u5220\u9664（\u8865\u5145）
\ndelete from \u88681\u7684\u522b\u540d,\u88682\u7684\u522b\u540d
\nfrom \u88681 \u522b\u540d
\ninner | left | right join \u88682 \u522b\u540d on \u8fde\u63a5\u6761\u4ef6
\nwhere \u7b5b\u9009\u6761\u4ef6<\/p>\n

truncate \u622a\u65ad\u8868
\n\u8bed\u6cd5\u683c\u5f0f：
\nTRUNCATE [TABLE] tbl_name<\/p>\n

delete VS truncate
\n（1）delete\u53ef\u4ee5\u52a0where\u6761\u4ef6，truncate\u4e0d\u53ef\u4ee5\u52a0where\u6761\u4ef6
\n（2）truncate\u5220\u9664，\u6548\u7387\u66f4\u9ad8
\n（3）\u5047\u5982\u8981\u5220\u9664\u7684\u8868\u4e2d\u6709\u81ea\u589e\u957f\u5217，\u5982\u679c\u7528delete\u5220\u9664\u540e，\u518d\u63d2\u5165\u6570\u636e，\u81ea\u589e\u957f\u5217\u7684\u503c\u4ece\u65ad\u70b9\u5f00\u59cb，
\n\u800ctruncate\u5220\u9664\u540e，\u518d\u63d2\u5165\u6570\u636e\u81ea\u589e\u957f\u5217\u7684\u503c\u4ece1\u5f00\u59cb\u3002
\n（4）truncate\u5220\u9664\u6ca1\u6709\u8fd4\u56de\u503c，delete\u5220\u9664\u6709\u8fd4\u56de\u503c
\n（5）truncate\u5220\u9664\u4e0d\u80fd\u56de\u6eda（\u4e8b\u52a1），delete\u5220\u9664\u53ef\u4ee5\u56de\u6eda\u3002
\n*\/<\/span>
\n# ###############################\u63d2\u5165#######################################<\/span>
\n— \u65b9\u5f0f\u4e00\u63d2\u5165：<\/span><\/p>\n

# eg:\u63d2\u5165\u7684\u503c\u7684\u7c7b\u578b\u8981\u4e0e\u5217\u7684\u7c7b\u578b\u4e00\u81f4\u6216\u517c\u5bb9<\/span>
\nINSERT<\/span> INTO<\/span> beauty (<\/span>id,<\/span>`<\/span>name`<\/span><\/span>,<\/span>sex,<\/span>borndate,<\/span>phone,<\/span>photo,<\/span>boyfriend_id)<\/span>–\u9519\u8bef<\/span>
\nVALUES<\/span> (<\/span>1<\/span>,<\/span>'\u8fea\u4e3d\u70ed\u5df4'<\/span>,<\/span>'\u5973'<\/span>,<\/span>'1992-06-03'<\/span>,<\/span>'17000000000'<\/span>,<\/span>NULL<\/span>,<\/span>1<\/span>)<\/span>;<\/span>
\n# eg:\u4e0d\u53ef\u4ee5\u4e3anull\u7684\u5217\u5fc5\u987b\u63d2\u5165\u503c，\u53ef\u4ee5\u4e3anull\u7684\u5982\u4f55\u63d2\u5165\u503c？ –\u9519\u8bef<\/span>
\nINSERT<\/span> INTO<\/span> beauty (<\/span>id,<\/span>`<\/span>name`<\/span><\/span>,<\/span>sex,<\/span>borndate,<\/span>phone,<\/span>photo,<\/span>boyfriend_id)<\/span>
\nVALUES<\/span> (<\/span>2<\/span>,<\/span>'\u8fea\u4e3d\u70ed\u5df4'<\/span>,<\/span>NULL<\/span>,<\/span>NULL<\/span>,<\/span>NULL<\/span>,<\/span>NULL<\/span>,<\/span>1<\/span>)<\/span>;<\/span><\/p>\n

INSERT<\/span> INTO<\/span> beauty (<\/span>id,<\/span>`<\/span>name`<\/span><\/span>,<\/span>sex,<\/span>boyfriend_id)<\/span> –\u53ef\u4ee5<\/span>
\nVALUES<\/span> (<\/span>3<\/span>,<\/span>'\u8d75\u4e3d\u9896'<\/span>,<\/span>'\u5973'<\/span>,<\/span>2<\/span>)<\/span>;<\/span>
\n# eg:\u5217\u7684\u987a\u5e8f\u662f\u5426\u53ef\u4ee5\u8c03\u6362？ \u53ef\u4ee5<\/span>
\nINSERT<\/span> INTO<\/span> beauty (<\/span>`<\/span>name`<\/span><\/span>,<\/span>sex,<\/span>id,<\/span>boyfriend_id)<\/span>
\nVALUES<\/span> (<\/span>'\u8d75\u4e3d\u98962'<\/span>,<\/span>'\u5973'<\/span>,<\/span>4<\/span>,<\/span>2<\/span>)<\/span>;<\/span>
\n# eg:\u5217\u6570\u548c\u503c\u7684\u4e2a\u6570\u662f\u5426\u5fc5\u987b\u4e00\u81f4？ \u5fc5\u987b\u4e00\u81f4<\/span>
\n— INSERT INTO beauty (id,`name`,sex,boyfriend_id)<\/span>
\n— VALUES (5,'\u8d75\u4e3d\u9896','\u5973',NULL,2);<\/span>
\n# eg:\u53ef\u4ee5\u7701\u7565\u5217\u540d，\u9ed8\u8ba4\u662f\u6240\u6709\u5217，\u800c\u4e14\u5217\u7684\u987a\u5e8f\u548c\u8868\u4e2d\u7684\u5217\u7684\u987a\u5e8f\u4e00\u81f4<\/span>
\nINSERT<\/span> INTO<\/span> beauty VALUES<\/span>(<\/span>6<\/span>,<\/span>'\u6768\u5e42'<\/span>,<\/span>'\u5973'<\/span>,<\/span>'1986-08-12'<\/span>,<\/span>'18000000000'<\/span>,<\/span>NULL<\/span>,<\/span>3<\/span>)<\/span>;<\/span>
\n# eg:\u53ef\u4ee5\u7701\u7565\u5217\u540d，\u9ed8\u8ba4\u662f\u6240\u6709\u5217，\u800c\u4e14\u5217\u7684\u987a\u5e8f\u548c\u8868\u4e2d\u7684\u5217\u7684\u987a\u5e8f\u4e00\u81f4<\/span>
\nINSERT<\/span> INTO<\/span> beauty VALUES<\/span>(<\/span>6<\/span>,<\/span>'\u6768\u5e42'<\/span>,<\/span>'\u5973'<\/span>,<\/span>'1986-08-12'<\/span>,<\/span>'18000000000'<\/span>,<\/span>NULL<\/span>,<\/span>3<\/span>)<\/span>;<\/span>
\nINSERT<\/span> INTO<\/span> beauty VALUES<\/span>(<\/span>7<\/span>,<\/span>'\u6768\u5e421'<\/span>,<\/span>'\u5973'<\/span>,<\/span>NULL<\/span>,<\/span>3<\/span>)<\/span>;<\/span>
\n— \u65b9\u5f0f\u4e8c\u63d2\u5165：<\/span><\/p>\n

insert<\/span> into<\/span> beauty
\nSET<\/span> id=<\/span>7<\/span>,<\/span>name=<\/span>'\u5218\u4ea6\u83f2'<\/span>,<\/span>sex=<\/span>'\u5973'<\/span>;<\/span><\/p>\n

insert<\/span> into<\/span> beauty
\nSET<\/span> name=<\/span>'\u5218\u4ea6\u83f2'<\/span>,<\/span>sex=<\/span>'\u5973'<\/span>;<\/span> — \u62a5\u9519<\/span><\/p>\n

— \u65b9\u5f0f\u4e00\u548c\u65b9\u5f0f\u4e8c\u5bf9\u6bd4<\/span><\/p>\n

INSERT<\/span> INTO<\/span> beauty VALUES<\/span>
\n(<\/span>8<\/span>,<\/span>'\u6768\u5e422'<\/span>,<\/span>'\u5973'<\/span>,<\/span>'1986-08-12'<\/span>,<\/span>'15000000000'<\/span>,<\/span>NULL<\/span>,<\/span>3<\/span>)<\/span>,<\/span>
\n(<\/span>9<\/span>,<\/span>'\u6768\u5e423'<\/span>,<\/span>'\u5973'<\/span>,<\/span>'1986-08-12'<\/span>,<\/span>'16000000000'<\/span>,<\/span>NULL<\/span>,<\/span>3<\/span>)<\/span>,<\/span>
\n(<\/span>10<\/span>,<\/span>'\u6768\u5e424'<\/span>,<\/span>'\u5973'<\/span>,<\/span>'1986-08-12'<\/span>,<\/span>'17000000000'<\/span>,<\/span>NULL<\/span>,<\/span>3<\/span>)<\/span>,<\/span>
\n(<\/span>11<\/span>,<\/span>'\u6768\u5e425'<\/span>,<\/span>'\u5973'<\/span>,<\/span>'1986-08-12'<\/span>,<\/span>'18000000000'<\/span>,<\/span>NULL<\/span>,<\/span>3<\/span>)<\/span>,<\/span>
\n(<\/span>12<\/span>,<\/span>'\u6768\u5e426'<\/span>,<\/span>'\u5973'<\/span>,<\/span>'1986-08-12'<\/span>,<\/span>'19000000000'<\/span>,<\/span>NULL<\/span>,<\/span>3<\/span>)<\/span>,<\/span>
\n(<\/span>13<\/span>,<\/span>'\u6768\u5e427'<\/span>,<\/span>'\u5973'<\/span>,<\/span>'1986-08-12'<\/span>,<\/span>'11000000000'<\/span>,<\/span>NULL<\/span>,<\/span>3<\/span>)<\/span>,<\/span>
\n(<\/span>14<\/span>,<\/span>'\u6768\u5e4278'<\/span>,<\/span>'\u5973'<\/span>,<\/span>'1986-08-12'<\/span>,<\/span>'12000000000'<\/span>,<\/span>NULL<\/span>,<\/span>3<\/span>)<\/span>;<\/span><\/p>\n

— insert into beauty <\/span>
\n— SET id=15,name='\u5218\u4ea6\u83f22',sex='\u5973',<\/span>
\n— SET id=16,name='\u5218\u4ea6\u83f23',sex='\u5973',<\/span>
\n— SET id=17,name='\u5218\u4ea6\u83f24',sex='\u5973';<\/span>
\n# ############################### \u4fee\u6539 #######################################<\/span>
\n# \u4fee\u6539\u5355 '1919999999'<\/span>
\nUPDATE<\/span> beauty SET<\/span> phone =<\/span> '1919999999'<\/span>
\nWHERE<\/span> name LIKE<\/span> '\u6768%'<\/span>;<\/span><\/p>\n

# eg:\u4fee\u6539boys\u8868\u4e2did\u4e3a 1 \u7684\u540d\u79f0\u4e3a：\u6c6a\u5cf02，\u9b45\u529b\u503c\u4e3a：10000<\/span>
\nUPDATE<\/span> boys set<\/span> boyName =<\/span> '\u6c6a\u5cf02'<\/span>,<\/span>userCP=<\/span>10000<\/span>
\nWHERE<\/span> id =<\/span> 1<\/span>;<\/span> <\/p>\n

# \u4fee\u6539\u591a\u8868\u8bb0\u5f55<\/span>
\n# eg:\u4fee\u6539\u6c6a\u5cf02\u5bf9\u5e94\u7684\u5973\u660e\u661f\u7684\u624b\u673a\u53f7\u4e3a911<\/span>
\nUPDATE<\/span> boys bo
\nINNER<\/span> JOIN<\/span> beauty b ON<\/span> bo.<\/span>id =<\/span> b.<\/span>boyfriend_id
\nSET<\/span> b.<\/span>phone =<\/span> '911'<\/span>
\nWHERE<\/span> bo.<\/span>boyName =<\/span> '\u6c6a\u5cf02'<\/span><\/p>\n

# eg:\u4fee\u6539\u6ca1\u6709\u7537\u670b\u53cb\u7684\u5973\u660e\u661f\u7684\u7537\u670b\u53cb\u7684\u7f16\u53f7\u4e3a 1<\/span>
\nupdate<\/span> boys bo
\nRIGHT<\/span> JOIN<\/span> beauty b ON<\/span> bo.<\/span>id =<\/span> b.<\/span>boyfriend_id
\nset<\/span> b.<\/span>boyfriend_id =<\/span> 1<\/span>
\nWHERE<\/span> bo.<\/span>id is<\/span> null<\/span>;<\/span>
\n# ###############################\u5220\u9664#######################################<\/span>
\n# \u5355\u8868\u5220\u9664<\/span>
\n# eg:\u5220\u9664\u624b\u673a\u53f7\u4ee591\u5f00\u5934\u7684\u5973\u795e\u4fe1\u606f<\/span>
\nDELETE<\/span> from<\/span> beauty WHERE<\/span> phone LIKE<\/span> '91%'<\/span>;<\/span><\/p>\n

# \u591a\u8868\u5220\u9664<\/span>
\n# \u5220\u9664\u5218\u607a\u5a01\u7684\u4fe1\u606f\u4ee5\u53ca\u4ed6\u5973\u670b\u53cb\u7684\u4fe1\u606f<\/span>
\nDELETE<\/span> b,<\/span>bo
\nFROM<\/span> beauty b
\nINNER<\/span> JOIN<\/span> boys bo ON<\/span> b.<\/span>boyfriend_id =<\/span> bo.<\/span>id
\nWHERE<\/span> bo.<\/span>boyName =<\/span> '\u5218\u607a\u5a01'<\/span>;<\/span>
\n# ############################### truncate \u5220\u9664#######################################<\/span>
\nSELECT<\/span> *<\/span> from<\/span> beauty;<\/span>
\nDELETE<\/span> FROM<\/span> beauty;<\/span>
\ntruncate<\/span> table<\/span> beauty;<\/span><\/p>\n

6，DDL\u8bed\u8a00 1\u3001\u5e93\u7684\u7ba1\u7406 \u521b\u5efa\u3001\u4fee\u6539\u3001\u5220\u9664 2\u3001\u8868\u7684\u7ba1\u7406 \u521b\u5efa\u3001\u4fee\u6539\u3001\u5220\u9664 3\u3001\u5e38\u89c1\u7684\u6570\u636e\u7c7b\u578b 4\u3001\u5e38\u89c1\u7684\u7ea6\u675f\u6761\u4ef6 （1），\u8868\u7ea7\u7ea6\u675f （2），\u5217\u7ea7\u7ea6\u675f 5\u3001\u81ea\u589e\u957f\u5217<\/p>\n

\/*
\n\u5e93\u7684\u7ba1\u7406
\n（1）\u5e93\u7684\u521b\u5efa\u8bed\u6cd5\u683c\u5f0f：
\ncreate database [if not exists] \u5e93\u540d;
\n（2）\u5e93\u7684\u4fee\u6539\u8bed\u6cd5\u683c\u5f0f：
\nalter_option: {
\n [DEFAULT] CHARACTER SET [=] charset_name
\n | [DEFAULT] COLLATE [=] collation_name
\n | [DEFAULT] ENCRYPTION [=] {'Y' | 'N'}
\n | READ ONLY [=] {DEFAULT | 0 | 1}
\n}
\n（3）\u5e93\u7684\u5220\u9664\u8bed\u6cd5\u683c\u5f0f：
\nDROP {DATABASE | SCHEMA} [IF EXISTS] db_name
\n\u8868\u7684\u7ba1\u7406
\n(1)\u521b\u5efa\u8868\u8bed\u6cd5\u683c\u5f0f：
\ncreate table \u8868\u540d(
\n \u5217\u540d \u5217\u7684\u7c7b\u578b[(\u957f\u5ea6) \u7ea6\u675f],
\n \u5217\u540d \u5217\u7684\u7c7b\u578b[(\u957f\u5ea6) \u7ea6\u675f],
\n \u5217\u540d \u5217\u7684\u7c7b\u578b[(\u957f\u5ea6) \u7ea6\u675f],
\n \u5217\u540d \u5217\u7684\u7c7b\u578b[(\u957f\u5ea6) \u7ea6\u675f],
\n \u5217\u540d \u5217\u7684\u7c7b\u578b[(\u957f\u5ea6) \u7ea6\u675f]
\n)
\n(2)\u4fee\u6539\u8868\u8bed\u6cd5\u683c\u5f0f：
\nalter table \u8868\u540d add | drop | modify | change column \u5217\u540d [\u5217\u7684\u7c7b\u578b \u7ea6\u675f];
\n(3)\u5220\u9664\u8868\u8bed\u6cd5\u683c\u5f0f：
\ndrop table [if exists] \u8868\u540d;
\n*\/<\/span>
\n# ##########################\u5e93\u7684\u7ba1\u7406_\u521b\u5efa###############################<\/span>
\n# eg:\u521b\u5efabigdata\u6570\u636e\u5e93<\/span>
\nCREATE<\/span> DATABASE<\/span> bigdata;<\/span><\/p>\n

CREATE<\/span> DATABASE<\/span> if<\/span> not<\/span> exists<\/span> bigdata;<\/span>
\n# ##########################\u5e93\u7684\u7ba1\u7406_\u4fee\u6539###############################<\/span>
\n#\u6ce8\u610f：\u4e0d\u5efa\u8bae\u4fee\u6539<\/span><\/p>\n

alter<\/span> database<\/span> bigdata character<\/span> set<\/span> 'utf8'<\/span>;<\/span><\/p>\n

ALTER<\/span> DATABASE<\/span> bigdata READ<\/span> ONLY =<\/span> 0<\/span>;<\/span> — 1\u53ea\u8bfb\u6a21\u5f0f<\/span>
\n— <\/span>
\n— SHOW CREATE DATABASE bigdata\\\\G; # \\\\G \u6807\u51c6\u5316\u8f93\u51fa<\/span>
\n# ##########################\u5e93\u7684\u7ba1\u7406_\u5220\u9664###############################<\/span>
\ndrop<\/span> DATABASE<\/span> if<\/span> exists<\/span> bigdata;<\/span><\/p>\n

# ##########################\u8868\u7684\u7ba1\u7406_\u521b\u5efa###############################<\/span>
\n# \u521b\u5efa\u6570\u636e\u5e93<\/span>
\ncreate<\/span> DATABASE<\/span> if<\/span> not<\/span> exists<\/span> book;<\/span>
\n# \u8fdb\u5165\u6570\u636e\u5e93<\/span>
\nuse<\/span> book;<\/span>
\n# \u521b\u5efa\u8868<\/span>
\ndrop<\/span> table<\/span> if<\/span> exists<\/span> book;<\/span>
\ncreate<\/span> TABLE<\/span> IF<\/span> NOT<\/span> EXISTS<\/span> book(<\/span>
\n id int<\/span>,<\/span> — \u7f16\u53f7<\/span>
\n bName varchar<\/span>(<\/span>255<\/span>)<\/span>,<\/span> — \u56fe\u4e66\u540d<\/span>
\n price double<\/span>,<\/span> — \u4ef7\u683c<\/span>
\n authorId int<\/span>,<\/span> — \u4f5c\u8005\u7f16\u53f7<\/span>
\n publishDate DATETIME<\/span> — \u51fa\u7248\u65e5\u671f<\/span>
\n)<\/span>;<\/span>
\n# \u67e5\u770b\u8868\u7ed3\u6784<\/span>
\ndesc<\/span> book;<\/span>
\n# \u521b\u5efa\u4f5c\u8005\u8868<\/span>
\ncreate<\/span> TABLE<\/span> IF<\/span> NOT<\/span> EXISTS<\/span> author(<\/span>
\n id int<\/span>,<\/span>
\n au_name VARCHAR<\/span>(<\/span>20<\/span>)<\/span>,<\/span>
\n nation VARCHAR<\/span>(<\/span>10<\/span>)<\/span>
\n)<\/span>;<\/span><\/p>\n

# \u67e5\u770b\u8868\u7ed3\u6784<\/span>
\ndesc<\/span> author;<\/span>
\n# ##########################\u8868\u7684\u7ba1\u7406_\u4fee\u6539###############################<\/span>
\n# \u4fee\u6539book\u8868\u7684\u5217\u540d <\/span>
\nalter<\/span> table<\/span> book CHANGE COLUMN<\/span> publishDate pubDate DATETIME<\/span>;<\/span>
\n# \u4fee\u6539\u5217\u7684\u7c7b\u578b\u6216\u7ea6\u675f<\/span>
\nalter<\/span> table<\/span> book MODIFY<\/span> COLUMN<\/span> pubDate TIMESTAMP<\/span>;<\/span>
\n# \u6dfb\u52a0\u65b0\u5217<\/span>
\nalter<\/span> table<\/span> author add<\/span> COLUMN<\/span> age int<\/span>;<\/span>
\n# \u5220\u9664\u5217<\/span>
\nALTER<\/span> TABLE<\/span> author DROP<\/span> COLUMN<\/span> age;<\/span>
\n# \u4fee\u6539\u8868\u540d<\/span>
\nALTER<\/span> TABLE<\/span> author RENAME<\/span> TO<\/span> book_author;<\/span>
\n#\u67e5\u770b\u8868\u4fe1\u606f<\/span>
\ndesc<\/span> book;<\/span>
\n# ##########################\u8868\u7684\u7ba1\u7406_\u5220\u9664###############################<\/span>
\nDROP<\/span> TABLE<\/span> if<\/span> EXISTS<\/span> book_author;<\/span>
\n# \u521b\u5efa\u4f5c\u8005\u8868 author<\/span>
\n# \u63d2\u5165\u6570\u636e\u5230\u4f5c\u8005\u8868 author<\/span>
\nINSERT<\/span> INTO<\/span> author VALUES<\/span>
\n(<\/span>1<\/span>,<\/span>'\u9c81\u8fc5'<\/span>,<\/span>'\u4e2d\u56fd'<\/span>)<\/span>,<\/span>
\n(<\/span>2<\/span>,<\/span>'\u83ab\u8a00'<\/span>,<\/span>'\u4e2d\u56fd'<\/span>)<\/span>,<\/span>
\n(<\/span>3<\/span>,<\/span>'\u4f59\u534e'<\/span>,<\/span>'\u4e2d\u56fd'<\/span>)<\/span>,<\/span>
\n(<\/span>4<\/span>,<\/span>'\u6751\u4e0a\u6625\u6811'<\/span>,<\/span>'\u65e5\u672c'<\/span>)<\/span>;<\/span>
\n# \u8868\u7684\u590d\u5236(\u8d4b\u503c\u8868\u7684\u7ed3\u6784 + \u6570\u636e) \u521b\u5efa\u8868\u7684\u4e00\u79cd\u65b9\u5f0f<\/span>
\nCREATE<\/span> TABLE<\/span> copy1 select<\/span> *<\/span> FROM<\/span> author;<\/span>
\n# \u8868\u7684\u590d\u5236(\u4ec5\u8d4b\u503c\u8868\u7684\u7ed3\u6784) \u521b\u5efa\u8868\u7684\u4e00\u79cd\u65b9\u5f0f<\/span>
\nCREATE<\/span> TABLE<\/span> copy2 like<\/span> author;<\/span>
\n# \u590d\u5236\u8868\u7684\u90e8\u5206\u6570\u636e<\/span>
\nCREATE<\/span> TABLE<\/span> copy3 SELECT<\/span>
\n id,<\/span>
\n au_name
\nFROM<\/span>
\n author
\nWHERE<\/span>
\n nation =<\/span> '\u4e2d\u56fd'<\/span>;<\/span><\/p>\n

# \u590d\u5236\u8868\u7684\u67d0\u4e9b\u5b57\u6bb5<\/span>
\nCREATE<\/span> TABLE<\/span> copy4
\nSELECT<\/span> id,<\/span>au_name from<\/span> author where<\/span> 0<\/span>;<\/span>#–\u4e0d\u590d\u5236\u6570\u636e<\/span><\/p>\n

CREATE<\/span> TABLE<\/span> copy5
\nSELECT<\/span> id,<\/span>au_name from<\/span> author where<\/span> 1<\/span>;<\/span>#\u5305\u542b\u6570\u636e<\/span><\/p>\n

# ##########################\u5e38\u89c1\u7684\u6570\u636e\u7c7b\u578b###############################<\/span>
\n\/*
\n\u6570\u503c\u6570\u636e\u7c7b\u578b：
\n \u6574\u6570\u7c7b\u578b：int\u3001bigint
\n \u5b9a\u70b9\u6570\u636e\u7c7b\u578b：decimal
\n \u6d6e\u70b9\u7c7b\u578b：float\u3001double<\/p>\n

\u65e5\u671f\u548c\u65f6\u95f4\u6570\u636e\u7c7b\u578b：date\u3001time\u3001datetime\u3001timestamp\u3001year<\/p>\n

\u5b57\u7b26\u4e32\u6570\u636e\u7c7b\u578b：char(0~255)\u3001varchar(0~65535)\u3001text\u3001blob(\u8f83\u957f\u7684\u4e8c\u8fdb\u5236\u6570\u636e) <\/p>\n

\u7ecf\u9a8c：\u5b57\u7b26\u7c7b\u578b：varchar(255)
\n*\/<\/span>
\n# ##########################\u5e38\u89c1\u7684\u7ea6\u675f\u6761\u4ef6###############################<\/span>
\n\/*
\n\u5e38\u89c1\u7684\u7ea6\u675f\u6761\u4ef6：
\n\u4e00\u79cd\u9650\u5236，\u7528\u4e8e\u9650\u5236\u8868\u4e2d\u7684\u6570\u636e，\u4e3a\u4e86\u4fdd\u8bc1\u8868\u4e2d\u7684\u6570\u636e\u7684\u51c6\u786e\u6027\u548c\u53ef\u9760\u6027\u3002
\n\u5e38\u89c1\u7ea6\u675f\u6761\u4ef6\u5206\u7c7b：
\n 1\u3001not null ：\u975e\u7a7a，\u7528\u4e8e\u4fdd\u8bc1\u8be5\u5b57\u6bb5\u7684\u503c\u4e0d\u80fd\u4e3a\u7a7a；\u6bd4\u5982：\u59d3\u540d\u3001\u5b66\u53f7\u7b49\u7b49
\n 2\u3001default：\u9ed8\u8ba4，\u7528\u4e8e\u4fdd\u8bc1\u8be5\u5b57\u6bb5\u6709\u9ed8\u8ba4\u503c；\u6bd4\u5982：\u6027\u522b\u7b49\u7b49
\n 3\u3001primary key：\u4e3b\u952e，\u7528\u4e8e\u4fdd\u8bc1\u8be5\u5b57\u6bb5\u7684\u503c\u5177\u6709\u552f\u4e00\u6027，\u5e76\u4e14\u975e\u7a7a；\u6bd4\u5982：\u5b66\u53f7\u3001\u5458\u5de5\u7f16\u53f7\u7b49\u7b49
\n 4\u3001unique:\u552f\u4e00，\u7528\u4e8e\u4fdd\u8bc1\u8be5\u5b57\u6bb5\u7684\u503c\u5177\u6709\u552f\u4e00\u6027，\u53ef\u4ee5\u4e3a\u7a7a；\u6bd4\u5982：\u5ea7\u4f4d\u53f7
\n 5\u3001check：\u68c0\u67e5\u7ea6\u675f；\u6bd4\u5982：\u5e74\u9f84\u3001\u6027\u522b
\n 6\u3001foreign key:\u5916\u952e，\u7528\u4e8e\u9650\u5236\u4e24\u4e2a\u8868\u7684\u5173\u7cfb\u7528\u4e8e\u4fdd\u8bc1\u8be5\u5b57\u6bb5\u7684\u503c\u5fc5\u987b\u6765\u81ea\u4e8e\u4e3b\u8868\u7684\u5173\u8054\u5217\u7684\u503c\u5728\u4ece\u8868
\n \u6dfb\u52a0\u5916\u952e\u7ea6\u675f，\u7528\u4e8e\u5f15\u7528\u4e3b\u8868\u4e2d\u67d0\u5217\u7684\u503c\u3002\u6bd4\u5982：\u5b66\u751f\u8868\u7684\u4e13\u4e1a\u7f16\u53f7\u3001\u5458\u5de5\u8868\u7684\u90e8\u95e8\u7f16\u53f7\u3001\u5458\u5de5\u8868\u5de5\u79cd\u7f16\u53f7\u3002<\/p>\n

\u6dfb\u52a0\u7ea6\u675f\u6761\u4ef6\u7684\u65f6\u673a：
\n 1\u3001\u521b\u5efa\u8868\u65f6\u6dfb\u52a0\u7ea6\u675f
\n 2\u3001\u4fee\u6539\u8868\u65f6\u6dfb\u52a0\u7ea6\u675f<\/p>\n

\u7ea6\u675f\u7684\u6dfb\u52a0\u5206\u7c7b：
\n\u5217\u7ea7\u7ea6\u675f：\u516d\u5927\u7ea6\u675f\u8bed\u6cd5\u4e0a\u90fd\u652f\u6301，\u4f46\u5916\u952e\u7ea6\u675f\u6ca1\u6709\u6548\u679c\u3002
\n\u8868\u7ea7\u7ea6\u675f：\u9664\u4e86\u975e\u7a7a\u3001\u9ed8\u8ba4\u7ea6\u675f，\u5176\u4ed6\u90fd\u652f\u6301\u3002<\/p>\n

\u6dfb\u52a0\u7ea6\u675f\u8bed\u6cd5\u683c\u5f0f\u5217\u7ea7\u7ea6\u675f：<\/p>\n

create table \u8868\u540d(
\n \u5217\u540d \u5217\u7684\u7c7b\u578b \u7ea6\u675f\u6761\u4ef6,
\n \u5217\u540d \u5217\u7684\u7c7b\u578b \u7ea6\u675f\u6761\u4ef6,
\n \u5217\u540d \u5217\u7684\u7c7b\u578b \u7ea6\u675f\u6761\u4ef6,
\n \u5217\u540d \u5217\u7684\u7c7b\u578b \u7ea6\u675f\u6761\u4ef6
\n….
\n)<\/p>\n

\u6dfb\u52a0\u7ea6\u675f\u8bed\u6cd5\u683c\u5f0f\u8868\u7ea7\u7ea6\u675f：
\ncreate table \u8868\u540d(
\n \u5217\u540d \u5217\u7684\u7c7b\u578b ,
\n \u5217\u540d \u5217\u7684\u7c7b\u578b ,
\n \u5217\u540d \u5217\u7684\u7c7b\u578b ,
\n \u5217\u540d \u5217\u7684\u7c7b\u578b
\n \u8868\u7ea7\u7ea6\u675f
\n….
\n)<\/p>\n

################################\u4e3b\u952e VS \u552f\u4e00 ################################
\n \u4fdd\u8bc1\u552f\u4e00\u6027 \u662f\u5426\u5141\u8bb8\u4e3a\u7a7a \u4e00\u4e2a\u8868\u4e2d\u53ef\u4ee5\u6709\u591a\u5c11\u4e2a \u662f\u5426\u5141\u8bb8\u7ec4\u5408
\n\u4e3b\u952e \u53ef\u4ee5 \u4e0d\u80fd \u81f3\u591a\u6709\u4e00\u4e2a \u5141\u8bb8，\u4f46\u4e0d\u63a8\u8350
\n\u552f\u4e00 \u53ef\u4ee5 \u53ef\u4ee5 \u53ef\u4ee5\u6709\u591a\u4e2a \u5141\u8bb8，\u4f46\u4e0d\u63a8\u8350<\/p>\n

\u5916\u952e\u8bbe\u7f6e\u6ce8\u610f：
\n 1\u3001\u8981\u6c42\u5728\u4ece\u8868\u4e2d\u8bbe\u7f6e\u5916\u952e\u5173\u7cfb
\n 2\u3001\u4ece\u8868\u7684\u5916\u952e\u5217\u7684\u7c7b\u578b\u548c\u4e3b\u8868\u7684\u5173\u8054\u5217\u7684\u7c7b\u578b\u8981\u6c42\u4e00\u81f4\u6216\u8005\u517c\u5bb9，\u540d\u79f0\u65e0\u8981\u6c42
\n 3\u3001\u4e3b\u8868\u7684\u5173\u8054\u5217\u5fc5\u987b\u662f\u4e00\u4e2akey（\u4e00\u822c\u662f\u4e3b\u952e\u6216\u8005\u552f\u4e00）
\n 4\u3001\u63d2\u5165\u6570\u636e\u65f6，\u5148\u63d2\u5165\u4e3b\u8868，\u518d\u63d2\u5165\u4ece\u8868，\u5220\u9664\u6570\u636e\u65f6，\u5148\u5220\u9664\u4ece\u8868，\u518d\u5220\u9664\u4e3b\u8868\u3002
\n*\/<\/span>
\n# ################################\u6dfb\u52a0\u5217\u7ea7\u7ea6\u675f################################<\/span>
\n\/*
\n\u8bed\u6cd5\u683c\u5f0f：\u76f4\u63a5\u5728\u5b57\u6bb5\u540d\u548c\u7c7b\u578b\u540e\u9762\u8ffd\u52a0 \u7ea6\u675f\u7c7b\u578b \u5373\u53ef\u3002
\ncreate table \u8868\u540d(
\n \u5217\u540d \u5217\u7684\u7c7b\u578b \u7ea6\u675f\u6761\u4ef6,
\n \u5217\u540d \u5217\u7684\u7c7b\u578b \u7ea6\u675f\u6761\u4ef6,
\n \u5217\u540d \u5217\u7684\u7c7b\u578b \u7ea6\u675f\u6761\u4ef6,
\n \u5217\u540d \u5217\u7684\u7c7b\u578b \u7ea6\u675f\u6761\u4ef6
\n….
\n)
\n\u53ea\u652f\u6301：\u9ed8\u8ba4\u3001\u975e\u7a7a\u3001\u4e3b\u952e\u3001\u552f\u4e00\u3001\u68c0\u67e5
\n*\/<\/span>
\n# \u521b\u5efa\u6570\u636e\u5e93<\/span>
\nCREATE<\/span> DATABASE<\/span> if<\/span> not<\/span> EXISTS<\/span> students;<\/span><\/p>\n

# \u8fdb\u5165\u6570\u636e\u5e93<\/span>
\nuse<\/span> students;<\/span><\/p>\n

# \u521b\u5efa\u5b66\u751f\u8868<\/span>
\n— drop table [if exists] \u8868\u540d;<\/span>
\ndrop<\/span> table<\/span> if<\/span> exists<\/span> stuinfo;<\/span>
\ncreate<\/span> table<\/span> if<\/span> not<\/span> exists<\/span> stuinfo(<\/span>
\n id int<\/span> primary<\/span> key<\/span>,<\/span> — \u4e3b\u952e\u7ea6\u675f<\/span>
\n stuName varchar<\/span>(<\/span>20<\/span>)<\/span> not<\/span> null<\/span> ,<\/span> — \u975e\u7a7a\u7ea6\u675f<\/span>
\n gender char<\/span>(<\/span>1<\/span>)<\/span> check<\/span>(<\/span>gender=<\/span>'\u7537'<\/span>OR<\/span> gender=<\/span>'\u5973'<\/span>)<\/span>,<\/span> — \u68c0\u67e5\u7ea6\u675f，mysql5.x\u4e0d\u652f\u6301<\/span>
\n seat int<\/span> unique<\/span>,<\/span> — \u552f\u4e00\u7ea6\u675f<\/span>
\n age int<\/span> default<\/span> 18<\/span>,<\/span> — \u9ed8\u8ba4\u7ea6\u675f<\/span>
\n — \u5916\u952e\u7ea6\u675f,\u5217\u7ea7\u7ea6\u675f\u4e2d\u4e0d\u751f\u6548\u7684<\/span>
\n majorId int<\/span> references<\/span> major(<\/span>id)<\/span>
\n)<\/span>;<\/span>
\n# \u521b\u5efa\u4e13\u4e1a\u8868<\/span>
\ndrop<\/span> table<\/span> if<\/span> exists<\/span> major;<\/span>
\ncreate<\/span> table<\/span> if<\/span> not<\/span> exists<\/span> major(<\/span>
\n id int<\/span> primary<\/span> key<\/span>,<\/span>
\n majorName varchar<\/span>(<\/span>20<\/span>)<\/span>
\n)<\/span>;<\/span>
\n# \u67e5\u770b\u7d22\u5f15,\u5305\u62ec：\u4e3b\u952e\u3001\u5916\u952e\u3001\u552f\u4e00<\/span>
\nshow<\/span> index<\/span> from<\/span> stuinfo;<\/span>
\n# ################################\u6dfb\u52a0\u8868\u7ea7\u7ea6\u675f################################<\/span>
\ndrop<\/span> table<\/span> if<\/span> exists<\/span> stuinfo;<\/span> — \u4ece\u8868<\/span>
\ncreate<\/span> table<\/span> if<\/span> not<\/span> exists<\/span> stuinfo(<\/span>
\n id int<\/span>,<\/span>
\n stuName varchar<\/span>(<\/span>20<\/span>)<\/span>,<\/span>
\n gender char<\/span>(<\/span>1<\/span>)<\/span>,<\/span>
\n seat int<\/span>,<\/span>
\n age int<\/span>,<\/span>
\n majorid int<\/span>,<\/span>
\n — \u4e3b\u952e\u7ea6\u675f pk\u7ea6\u675f\u540d\u79f0<\/span>
\n CONSTRAINT<\/span> pk primary<\/span> key<\/span>(<\/span>id)<\/span>,<\/span> — \u4e3b\u952e<\/span>
\n CONSTRAINT<\/span> uq unique<\/span>(<\/span>seat)<\/span>,<\/span> — \u552f\u4e00<\/span>
\n CONSTRAINT<\/span> ck check<\/span>(<\/span>gender=<\/span>'\u7537'<\/span>OR<\/span> gender=<\/span>'\u5973'<\/span>)<\/span>,<\/span> — \u68c0\u67e5<\/span>
\n CONSTRAINT<\/span> fk_stuinfo_major foreign<\/span> key<\/span>(<\/span>majorid)<\/span> REFERENCES<\/span> major(<\/span>id)<\/span> — \u5916\u952e<\/span>
\n)<\/span>;<\/span>
\n# 4\u3001\u63d2\u5165\u6570\u636e\u65f6，\u5148\u63d2\u5165\u4e3b\u8868，\u518d\u63d2\u5165\u4ece\u8868，\u5220\u9664\u6570\u636e\u65f6，\u5148\u5220\u9664\u4ece\u8868，\u518d\u5220\u9664\u4e3b\u8868\u3002<\/span>
\ndesc<\/span> stuinfo;<\/span><\/p>\n

# \u67e5\u770b\u7d22\u5f15\u5305\u542b：\u4e3b\u952e\u3001\u552f\u4e00\u3001\u5916\u952e<\/span>
\nshow<\/span> index<\/span> from<\/span> stuinfo;<\/span>
\n# ########################\u4fee\u6539\u8868\u65f6\u6dfb\u52a0\u7ea6\u675f\u6761\u4ef6#########################<\/span>
\n# \u5220\u9664\u975e\u7a7a\u7ea6\u675f<\/span>
\nalter<\/span> table<\/span> stuinfo modify<\/span> column<\/span> stuName varchar<\/span>(<\/span>20<\/span>)<\/span> null<\/span>;<\/span><\/p>\n

# \u5220\u9664\u9ed8\u8ba4\u7ea6\u675f<\/span>
\nalter<\/span> table<\/span> stuinfo modify<\/span> column<\/span> age int<\/span>;<\/span><\/p>\n

# \u5220\u9664\u4e3b\u952e<\/span>
\nalter<\/span> table<\/span> stuinfo drop<\/span> primary<\/span> key<\/span>;<\/span><\/p>\n

# \u5220\u9664\u552f\u4e00 \u5220\u9664\u7684\u662f\u7d22\u5f15 index<\/span>
\nalter<\/span> table<\/span> stuinfo drop<\/span> index<\/span> seat;<\/span><\/p>\n

# \u5220\u9664\u5916\u952e<\/span>
\n# \u6ce8\u610f：\u5728\u8bbe\u7f6e\u5916\u952e\u7ea6\u675f\u7684\u65f6\u5019，\u5efa\u8bae\u7ed9\u522b\u540d！！！<\/span>
\nalter<\/span> table<\/span> stuinfo drop<\/span> foreign<\/span> key<\/span> stuinfo_ibfk_1;<\/span><\/p>\n

desc<\/span> stuinfo;<\/span>
\nshow<\/span> index<\/span> from<\/span> stuinfo;<\/span><\/p>\n

SELECT<\/span>
\n CONSTRAINT_NAME,<\/span>
\n COLUMN_NAME,<\/span>
\n REFERENCED_TABLE_NAME,<\/span>
\n REFERENCED_COLUMN_NAME
\nFROM<\/span>
\n INFORMATION_SCHEMA.<\/span>KEY_COLUMN_USAGE
\nWHERE<\/span>
\n TABLE_SCHEMA =<\/span> 'students'<\/span>
\n AND<\/span> TABLE_NAME =<\/span> 'stuinfo'<\/span>
\n AND<\/span> REFERENCED_TABLE_NAME IS<\/span> NOT<\/span> NULL<\/span>;<\/span>
\n# ########################\u81ea\u589e\u957f\u5217###########################################<\/span>
\n# （\u6807\u8bc6\u5217）\u81ea\u589e\u957f\u5217<\/span>
\n\/*
\n\u81ea\u589e\u957f\u5217：\u53ef\u4ee5\u4e0d\u7528\u624b\u52a8\u7684\u63d2\u5165\u503c，\u7cfb\u7edf\u63d0\u4f9b\u9ed8\u8ba4\u7684\u5e8f\u5217\u503c
\n\u7279\u70b9：
\n1\u3001\u6807\u8bc6\u5217\u5fc5\u987b\u548c\u4e3b\u952e\u642d\u914d？\u4e0d\u4e00\u5b9a，\u4f46\u8981\u6c42\u662f\u4e00\u4e2akey
\n2\u3001\u4e00\u4e2a\u8868\u4e2d\u6709\u51e0\u4e2a\u6807\u8bc6\u5217？\u81f3\u591a\u4e00\u4e2a
\n3\u3001\u6807\u8bc6\u5217\u7684\u7c7b\u578b\u53ea\u80fd\u662f\u6570\u503c\u7c7b\u578b
\n4\u3001\u6807\u8bc6\u5217\u53ef\u4ee5\u901a\u8fc7 set auto_inrement_increment = xxx;\u8bbe\u7f6e
\n*\/<\/span>
\n# AUTO_INCREMENT<\/span>
\n# \u67e5\u770b\u9ed8\u8ba4\u6b65\u957f<\/span>
\nSHOW<\/span> VARIABLES LIKE<\/span> '%auto_increment%'<\/span>;<\/span>
\n# \u521b\u5efa\u8868\u65f6，\u8bbe\u7f6e\u81ea\u589e\u957f\u5217<\/span>
\ncreate<\/span> table<\/span> tab_stu(<\/span>
\n id int<\/span> primary<\/span> key<\/span> auto_increment<\/span>,<\/span>
\n name varchar<\/span>(<\/span>20<\/span>)<\/span>
\n)<\/span>;<\/span><\/p>\n

insert<\/span> into<\/span> tab_stu values<\/span>(<\/span>null<\/span>,<\/span>'\u5f20\u4e09'<\/span>)<\/span>;<\/span>
\nselect<\/span> *<\/span> from<\/span> tab_stu;<\/span>
\nset<\/span> auto_increment_increment =<\/span> 3<\/span>;<\/span>
\n# \u6ce8\u610f：\u53ea\u5141\u8bb8\u8bbe\u7f6e\u6b65\u957f，\u4e0d\u5141\u8bb8\u8bbe\u7f6e\u504f\u79fb\u91cf<\/span>
\ninsert<\/span> into<\/span> tab_stu values<\/span>
\n(<\/span>null<\/span>,<\/span>'\u5f20\u4e091'<\/span>)<\/span>,<\/span>
\n(<\/span>null<\/span>,<\/span>'\u5f20\u4e092'<\/span>)<\/span>,<\/span>
\n(<\/span>null<\/span>,<\/span>'\u5f20\u4e093'<\/span>)<\/span>,<\/span>
\n(<\/span>null<\/span>,<\/span>'\u5f20\u4e094'<\/span>)<\/span>,<\/span>
\n(<\/span>null<\/span>,<\/span>'\u5f20\u4e095'<\/span>)<\/span>;<\/span><\/p>\n

6，DCL（\u4e8b\u52a1\u63a7\u5236\u8bed\u97f3） \u4e8b\u52a1：\u4e00\u4e2a\u6216\u8005\u4e00\u7ec4sql\u8bed\u53e5\u7ec4\u6210\u7684\u4e00\u4e2a\u6267\u884c\u5355\u5143，\u8fd9\u4e2a\u6267\u884c\u5355\u5143\u8981\u4e48\u5168\u90e8\u6267\u884c，\u8981\u4e48\u5168\u90e8\u4e0d\u6267\u884c\u3002 \u7ecf\u5178\u6848\u4f8b：\u94f6\u884c\u8f6c\u88c5 \u5170\u667a 1000 \u6570\u52a0 1000 update \u8868 set \u5170\u667a\u4f59\u989d = 500 where name = \u2018\u5170\u667a\u2019 \u610f\u5916 update \u8868 set \u6570\u52a0\u4f59\u989d = 500 where name = \u2018\u6570\u52a0\u2019<\/p>\n

\u4e8b\u52a1\u7279\u6027：ACID \u539f\u5b50\u6027（A）：\u4e00\u4e2a\u4e8b\u52a1\u4e0d\u53ef\u4ee5\u518d\u5206\u5272，\u8981\u4e48\u90fd\u6267\u884c\u8981\u4e48\u90fd\u4e0d\u6267\u884c\u3002 \u4e00\u81f4\u6027（C）:\u4e00\u4e2a\u4e8b\u52a1\u6267\u884c\u4f1a\u4f7f\u6570\u636e\u4ece\u4e00\u4e2a\u4e00\u81f4\u72b6\u6001\u5207\u6362\u5230\u53e6\u4e00\u4e2a\u4e00\u81f4\u72b6\u6001\u3002 \u9694\u79bb\u6027（I）:\u4e00\u4e2a\u4e8b\u52a1\u7684\u6267\u884c\u4e0d\u53d7\u5176\u4ed6\u4e8b\u52a1\u7684\u5e72\u6270 \u6301\u4e45\u6027（D）:\u4e00\u4e2a\u4e8b\u52a1\u4e00\u65e6\u63d0\u4ea4，\u5219\u4f1a\u6c38\u4e45\u7684\u6539\u53d8\u6570\u636e\u5e93\u7684\u6570\u636e<\/p>\n

\u4e8b\u7269\u9694\u79bb\u7ea7\u522b （\u8bfb\u672a\u63d0\u4ea4）READ UNCOMMITTED （\u8bfb\u63d0\u4ea4）READ COMMITTED （\u53ef\u91cd\u590d\u8bfb）REPEATABLE READ \u2013 MySQL\u9ed8\u8ba4 （\u4e32\u884c\u5316）SERIALIZABLE<\/p>\n

\u67e5\u770bmysql\u9694\u79bb\u7ea7\u522b select @@transaction_isolation;<\/p>\n

\u8bbe\u7f6e\u9694\u79bb\u7ea7\u522b： set session | global transaction isolation level \u9694\u79bb\u7ea7\u522b;<\/p>\n

set session transaction isolation level READ UNCOMMITTED; set session transaction isolation level READ COMMITTED; set session transaction isolation level REPEATABLE READ; set session transaction isolation level SERIALIZABLE;<\/p>\n

\u89c6\u56fe\u7ba1\u7406 \u521b\u5efa\u3001\u4fee\u6539\u3001\u5220\u9664<\/p>\n

\/*
\n\u4e8b\u52a1\u7684\u521b\u5efa：
\n（1）\u9690\u5f0f\u4e8b\u52a1：\u4e8b\u52a1\u6ca1\u6709\u660e\u663e\u7684\u5f00\u59cb\u548c\u7ed3\u675f\u6807\u8bb0
\n\u6bd4\u5982：insert\u3001update\u3001delete
\n（2）\u663e\u793a\u4e8b\u52a1：\u4e8b\u52a1\u5177\u6709\u660e\u663e\u7684\u5f00\u542f\u548c\u7ed3\u675f\u7684\u6807\u8bb0
\n\u524d\u63d0：\u5fc5\u987b\u5148\u8bbe\u7f6e\u81ea\u52a8\u63d0\u4ea4\u529f\u80fd\u4e3a\u7981\u7528
\nset autocommit = 0;
\n# \u6b65\u9aa4\u4e00：\u5f00\u542f\u4e8b\u52a1
\nset autocommit = 0;
\nstart transaction; — \u53ef\u9009\u7684<\/p>\n

# \u6b65\u9aa4\u4e8c：\u7f16\u5199\u4e8b\u52a1\u4e2d\u7684SQL\u8bed\u53e5
\n（select\u3001insert\u3001update\u3001delete）
\n\u8bed\u53e51；
\n\u8bed\u53e52；
\n…..<\/p>\n

# \u6b65\u9aa4\u4e09：\u7ed3\u675f\u4e8b\u52a1
\ncommit;\u63d0\u4ea4\u4e8b\u52a1
\nrollback;\u56de\u6eda\u4e8b\u52a1
\nsavepoint \u8282\u70b9\u540d; \u8bbe\u7f6e\u4fdd\u5b58\u70b9
\n*\/<\/span><\/p>\n

# \u67e5\u770bmysql\u5f15\u64ce # mysql\u9ed8\u8ba4\u5f15\u64ce InnoDB<\/span>
\nshow<\/span> engines;<\/span><\/p>\n

# \u67e5\u770bmysql\u4e8b\u52a1\u662f\u5426\u5f00\u542f<\/span>
\nshow<\/span> variables like<\/span> 'autocommit'<\/span>;<\/span><\/p>\n

— \u521b\u5efa\u8868<\/span>
\ndrop<\/span> table<\/span> if<\/span> exists<\/span> account;<\/span>
\nCREATE<\/span> TABLE<\/span> account(<\/span>
\n id int<\/span> primary<\/span> key<\/span> auto_increment<\/span>,<\/span>
\n username varchar<\/span>(<\/span>20<\/span>)<\/span>,<\/span>
\n balance DOUBLE<\/span>
\n)<\/span>;<\/span><\/p>\n

— \u63d2\u5165\u6570\u636e<\/span>
\nINSERT<\/span> INTO<\/span> account (<\/span> username,<\/span> balance )<\/span> VALUES<\/span>
\n(<\/span> '\u5170\u667a'<\/span>,<\/span> 1000<\/span> )<\/span>,<\/span>
\n(<\/span> '\u6570\u52a0'<\/span>,<\/span> 1000<\/span> )<\/span>;<\/span><\/p>\n

set<\/span> auto_increment_increment =<\/span> 1<\/span>;<\/span><\/p>\n

# \u6f14\u793a\u4e8b\u52a1<\/span><\/p>\n

set<\/span> autocommit=<\/span>0<\/span>;<\/span>
\nstart<\/span> transaction<\/span>;<\/span><\/p>\n

update<\/span> account set<\/span> balance =<\/span> 500<\/span> where<\/span> username =<\/span> '\u5170\u667a'<\/span>;<\/span>
\nupdate<\/span> account set<\/span> balance =<\/span> 1500<\/span> where<\/span> username=<\/span>'\u6570\u52a0'<\/span>;<\/span><\/p>\n

commit<\/span>;<\/span><\/p>\n

select<\/span> *<\/span> from<\/span> account;<\/span>
\n\/*
\n\u4e8b\u52a1\u9694\u79bb\u7ea7\u522b：
\n（\u8bfb\u672a\u63d0\u4ea4）READ UNCOMMITTED
\n（\u8bfb\u63d0\u4ea4）READ COMMITTED
\n（\u53ef\u91cd\u590d\u8bfb）REPEATABLE READ — MySQL\u9ed8\u8ba4
\n（\u4e32\u884c\u5316）SERIALIZABLE<\/p>\n

\u9694\u79bb\u7ea7\u522b \u810f\u8bfb \u4e0d\u53ef\u91cd\u590d\u8bfb \u5e7b\u8bfb \u5b9e\u73b0\u65b9\u5f0f
\nREAD UNCOMMITTED \u2705 \u2705 \u2705 \u8bfb\u672a\u63d0\u4ea4\u6570\u636e
\nREAD COMMITTED \u274c \u2705 \u2705 \u6bcf\u6b21\u8bfb\u751f\u6210\u65b0\u5feb\u7167
\nREPEATABLE READ（\u9ed8\u8ba4） \u274c \u274c \u2705 \u4e8b\u52a1\u5185\u4f7f\u7528\u540c\u4e00\u5feb\u7167
\nSERIALIZABLE \u274c \u274c \u274c \u5f3a\u5236\u52a0\u9501\u4e32\u884c\u6267\u884c<\/p>\n

\u67e5\u770bmysql\u9694\u79bb\u7ea7\u522b
\nselect @@transaction_isolation;<\/p>\n

\u8bbe\u7f6e\u9694\u79bb\u7ea7\u522b：
\nset session | global transaction isolation level \u9694\u79bb\u7ea7\u522b;<\/p>\n

set session transaction isolation level READ UNCOMMITTED;
\nset session transaction isolation level READ COMMITTED;
\nset session transaction isolation level REPEATABLE READ;
\nset session transaction isolation level SERIALIZABLE;
\n*\/<\/span>
\n# \u67e5\u770bmysql\u9694\u79bb\u7ea7\u522b # REPEATABLE-READ<\/span>
\nselect<\/span> @@transaction_isolation<\/span>;<\/span><\/p>\n

# \u7b2c\u4e00\u79cd：<\/span>
\nset<\/span> session<\/span> transaction<\/span> isolation<\/span> level<\/span> READ<\/span> COMMITTED<\/span>;<\/span>
\nset<\/span> autocommit=<\/span>0<\/span>;<\/span>
\nstart<\/span> transaction<\/span>;<\/span><\/p>\n

update<\/span> account set<\/span> balance =<\/span> 1000<\/span> where<\/span> username =<\/span> '\u5170\u667a'<\/span>;<\/span>
\nupdate<\/span> account set<\/span> balance =<\/span> 1000<\/span> where<\/span> username=<\/span>'\u6570\u52a0'<\/span>;<\/span><\/p>\n

commit<\/span>;<\/span><\/p>\n

select<\/span> *<\/span> from<\/span> account;<\/span><\/p>\n

# \u7b2c\u4e8c\u79cd：<\/span>
\nset<\/span> session<\/span> transaction<\/span> isolation<\/span> level<\/span> READ<\/span> UNCOMMITTED<\/span>;<\/span>
\nselect<\/span> @@transaction_isolation<\/span>;<\/span>
\nset<\/span> autocommit=<\/span>0<\/span>;<\/span>
\nstart<\/span> transaction<\/span>;<\/span><\/p>\n

update<\/span> account set<\/span> balance =<\/span> 1000<\/span> where<\/span> username =<\/span> '\u5170\u667a'<\/span>;<\/span>
\nupdate<\/span> account set<\/span> balance =<\/span> 1000<\/span> where<\/span> username=<\/span>'\u6570\u52a0'<\/span>;<\/span><\/p>\n

commit<\/span>;<\/span><\/p>\n

select<\/span> *<\/span> from<\/span> account;<\/span><\/p>\n

# \u7b2c\u56db\u79cd：<\/span>
\nset<\/span> session<\/span> transaction<\/span> isolation<\/span> level<\/span> SERIALIZABLE<\/span>;<\/span><\/p>\n

select<\/span> @@transaction_isolation<\/span>;<\/span>
\nset<\/span> autocommit=<\/span>0<\/span>;<\/span>
\nstart<\/span> transaction<\/span>;<\/span><\/p>\n

update<\/span> account set<\/span> balance =<\/span> 1000<\/span> where<\/span> username =<\/span> '\u5170\u667a'<\/span>;<\/span>
\nupdate<\/span> account set<\/span> balance =<\/span> 1000<\/span> where<\/span> username=<\/span>'\u6570\u52a0'<\/span>;<\/span><\/p>\n

commit<\/span>;<\/span><\/p>\n

select<\/span> *<\/span> from<\/span> account;<\/span><\/p>\n

\/*
\n\u8bbe\u7f6e\u4fdd\u5b58\u70b9savepoint
\nset autocommit=0;
\nstart transaction;
\ndelete from account where id = 1;
\n— \u8bbe\u7f6e\u4fdd\u5b58\u70b9
\nsavepoint a;
\ndelete from account where id = 2;
\nrollback to a;
\n*\/<\/span>
\n\/*
\n\u89c6\u56fe:\u865a\u62df\u8868，\u548c\u666e\u901a\u8868\u4e00\u6837\u4f7f\u7528，\u901a\u8fc7\u8868\u52a8\u6001\u751f\u6210\u6570\u636e\u3002
\n\u89c6\u56fe\u8bed\u6cd5\u683c\u5f0f：
\nCREATE
\n [OR REPLACE]
\n [ALGORITHM = {UNDEFINED | MERGE | TEMPTABLE}]
\n [DEFINER = user]
\n [SQL SECURITY { DEFINER | INVOKER }]
\n VIEW view_name [(column_list)]
\n AS select_statement
\n [WITH [CASCADED | LOCAL] CHECK OPTION]<\/p>\n

*\/<\/span>
\nselect<\/span> *<\/span> from<\/span> myemployees.<\/span>employees;<\/span><\/p>\n

select<\/span>
\n stuname,<\/span>
\n gender,<\/span>
\n seat,<\/span>
\n age,<\/span>
\n majorid
\nFROM<\/span>
\n stuinfo
\nWHERE<\/span>
\n stuName like<\/span> '\u5f20%'<\/span>;<\/span><\/p>\n

— \u521b\u5efa\u89c6\u56fe<\/span>
\ncreate<\/span> view<\/span> myv1
\nAS<\/span>
\nSELECT<\/span>
\n stuname,<\/span>
\n majorname
\nFROM<\/span>
\n stuinfo s
\nINNER<\/span> JOIN<\/span> major m ON<\/span> s.<\/span>majorid =<\/span> m.<\/span>id
\nwhere<\/span>
\n s.<\/span>stuName like<\/span> '\u5f20%'<\/span>;<\/span><\/p>\n

select<\/span> *<\/span> from<\/span> myv1;<\/span><\/p>\n

\/*
\n\u4fee\u6539\u89c6\u56fe：
\n\u8bed\u6cd5\u683c\u5f0f：
\nALTER
\n [ALGORITHM = {UNDEFINED | MERGE | TEMPTABLE}]
\n [DEFINER = user]
\n [SQL SECURITY { DEFINER | INVOKER }]
\n VIEW view_name [(column_list)]
\n AS select_statement
\n [WITH [CASCADED | LOCAL] CHECK OPTION]
\n*\/<\/span><\/p>\n

alter<\/span> view<\/span> myv1
\nAS<\/span>
\nselect<\/span> *<\/span> from<\/span> stuinfo;<\/span><\/p>\n

\/*
\n\u5220\u9664\u89c6\u56fe
\n\u8bed\u6cd5\u683c\u5f0f：
\nDROP VIEW [IF EXISTS]
\n view_name [, view_name] …
\n [RESTRICT | CASCADE]
\n*\/<\/span><\/p>\n

drop<\/span> view<\/span> if<\/span> exists<\/span> myv1;<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

\u4e00，\u6570\u636e\u5e93
\n1，\u6570\u636e\u5e93\u7684\u597d\u5904： （1）\u5b9e\u73b0\u6570\u636e\u6301\u4e45\u5316 （2）\u4f7f\u7528\u5b8c\u6574\u7684\u7ba1\u7406\u7cfb\u7edf\u540c\u610f\u7ba1\u7406，\u4fbf\u4e8e\u67e5\u8be2 2，\u6570\u636e\u5e93\u7684\u6982\u5ff5 （1）\u6570\u636e\u5e93（database）\u7b80\u79f0 DB （2）\u6570\u636e\u5e93\u7ba1\u7406\u7cfb\u7edf（DBMS) （3）\u7ed3\u6784\u5316\u67e5\u8be2\u8bed\u8a00(SQL) <\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[114,100],"topic":[],"class_list":["post-100603","post","type-post","status-publish","format-standard","hentry","category-server","tag-mysql","tag-100"],"yoast_head":"\nMySQL - \u7f51\u7855\u4e92\u8054\u5e2e\u52a9\u4e2d\u5fc3<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.wsisp.com\/helps\/100603.html\" \/>\n<meta property=\"og:locale\" content=\"zh_CN\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"MySQL - 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